Inequitable conduct is the rare patent defense that can destroy an entire patent rather than a single claim. It does not narrow a monopoly; it dissolves it. A finding can sweep in claims that were never asserted, infect sister patents in the same family, expose the patent owner to an exceptional-case fee award, strip away the attorney-client privilege through the crime-fraud exception, and even seed an antitrust counterclaim. That is why practitioners call it the "atomic bomb" of patent law, and why courts have spent more than a decade trying to keep it holstered. Our companion article, Inequitable Conduct in Patent Prosecution -- Navigating the Atomic Bomb of Patent Law, lays out the doctrine: what it is, why the Federal Circuit reined it in, and how the elements fit together.

This piece is the litigator's companion. It is about the work. Where do you actually dig to find evidence that a patent applicant misled the United States Patent and Trademark Office (USPTO)? How do you turn a suspicion into a pleading that survives a motion to dismiss? How do you frame discovery, deal with privilege, deploy experts, and carry a clear-and-convincing burden at trial? And, just as important, if you represent the patent owner, how do you see the attack coming and blunt it before it lands?

This article answers those questions in plain language. By the end you will understand the duty of candor at 37 C.F.R. Section 1.56 and the people it binds; the heightened pleading standard of Exergen Corp. v. Wal-Mart Stores, Inc., 575 F.3d 1312 (Fed. Cir. 2009), under Federal Rule of Civil Procedure 9(b); the demanding substantive test of Therasense, Inc. v. Becton, Dickinson & Co., 649 F.3d 1276 (Fed. Cir. 2011) (en banc); the concrete places where evidence hides; a workable discovery plan; the privilege and prosecution-bar landmines that surround this defense; and how the proof comes together at trial. Hypotheticals throughout use clearly invented companies such as "Acme Corp." and "Beacon Devices" to make the doctrine concrete.

A Fast Orientation: The Doctrine in One Section

Before you can find evidence of inequitable conduct, you have to know what you are looking for. The legal target is narrow, and the narrowness is deliberate.

Every person substantively involved in preparing or prosecuting a U.S. patent application owes the USPTO a duty of candor and good faith -- a duty to deal honestly with the patent examiner and to disclose information known to be material to whether the claimed invention deserves a patent. That duty is codified at 37 C.F.R. Section 1.56 (often called "Rule 56"), reinforced by the practitioner's professional-responsibility obligations at 37 C.F.R. Section 11.303, and explained in the USPTO's Manual of Patent Examining Procedure (MPEP) Sections 2000-2016. Critically, the duty runs individually to each prosecuting attorney or patent agent, to each named inventor (who must acknowledge the duty in the inventor's declaration under 37 C.F.R. Section 1.63(c)), and to anyone else associated with the inventor, attorney, agent, or assignee who is substantively involved -- including in-house counsel who feeds references to outside prosecution counsel. See 37 C.F.R. Section 1.56(c); MPEP Section 2001.01. The duty persists throughout prosecution, including after a notice of allowance and before the patent issues. 37 C.F.R. Section 1.56(a); MPEP Section 2001.04.

When that duty is breached badly enough, a court can declare the patent unenforceable -- not invalid as to one claim, but unenforceable in its entirety, and sometimes across an entire patent family. The remedy is not money damages; it is the obliteration of the patent right. The USPTO itself generally does not police duty-of-candor violations (MPEP Section 2010), so the enforcement engine is the litigation defense raised by an accused infringer under 35 U.S.C. Section 282(b)(1).

In Therasense, the en banc Federal Circuit tightened the standard precisely to stop the doctrine from being pleaded reflexively in nearly every patent case. After Therasense, a challenger must prove, by clear and convincing evidence, two separate elements:

  1. But-for materiality -- that the USPTO would not have allowed the claim had it been aware of the withheld or misrepresented information (Therasense, 649 F.3d at 1291); and
  2. Specific intent to deceive -- that the duty-bearer knew of the information, knew it was material, and made a deliberate decision to withhold or misrepresent it (id. at 1290).

Two refinements matter for the evidence hunt. First, Therasense killed the old "sliding scale," under which a strong showing of materiality could make up for a weak showing of intent, and vice versa (id. at 1290). The elements are now independent; you must build each one on its own footing. Second, the court carved out an exception: where the applicant engaged in affirmative egregious misconduct, such as filing an "unmistakably false affidavit," but-for materiality is presumed and need not be separately proven (id. at 1292; see also Intellect Wireless, Inc. v. HTC Corp., 732 F.3d 1339, 1344 (Fed. Cir. 2013); TransWeb, LLC v. 3M Innovative Properties Co., 812 F.3d 1295, 1304 (Fed. Cir. 2016)). This egregious-conduct path is the litigator's friend, because false declarations leave a documentary trail and shorten the proof.

The proof-of-intent rule is unusually strict and shapes everything you do as an investigator. Because direct evidence of intent -- a memo saying "let's hide this from the examiner" -- is almost never available, courts permit intent to be inferred from circumstantial evidence. But the deceptive-intent inference must be "the single most reasonable inference able to be drawn from the evidence" (Therasense, 649 F.3d at 1290; Ohio Willow Wood Co. v. Alps South, LLC, 735 F.3d 1333, 1351 (Fed. Cir. 2013)). If the record supports an equally plausible innocent explanation -- oversight, negligence, even gross negligence, or a reasonable judgment call about materiality -- the defense fails. Negligence is not deceit, and a "suspicious omission" is not enough (Ohio Willow Wood, 735 F.3d at 1351). And the patentee does not even have to offer a good-faith explanation until the challenger has shown a threshold level of deceptive intent (Therasense, 649 F.3d at 1291). Your job, therefore, is not just to find a withheld reference. It is to assemble facts that make deceit the only sensible reading of the record.

With that target in mind, the rest of this article is about how to hit it.

Step One: Pleading Inequitable Conduct Under Rule 9(b) and Exergen

You cannot get to discovery -- where most of the real evidence lives -- unless your pleading survives. And inequitable conduct is held to a heightened pleading standard because it sounds in fraud.

Why Rule 9(b) Applies

Federal Rule of Civil Procedure 9(b) requires that "in alleging fraud or mistake, a party must state with particularity the circumstances constituting fraud or mistake." In Exergen, the Federal Circuit held that inequitable conduct, "while a broader concept than fraud, must be pled with particularity under Rule 9(b)" (575 F.3d at 1326-27). That holding governs nationwide, because the Federal Circuit applies its own law to the substance of inequitable conduct even when it borrows a regional circuit's general Rule 9(b) framework for matters of pure procedure.

The practical consequence is severe. A conclusory allegation that "the applicant withheld material prior art with intent to deceive the PTO" will be stricken or dismissed. So will boilerplate that gestures at "the inventors and/or their attorneys." If you represent an accused infringer, Exergen is the gate you must clear before you ever see the patentee's documents. If you represent the patentee, Exergen is your first -- and often best -- opportunity to knock the defense out cheaply.

The Exergen Checklist: Who, What, When, Where, Why, and How

Exergen requires the pleading to identify "the specific who, what, when, where, and how" of the material misrepresentation or omission committed before the USPTO, plus underlying facts from which the court may reasonably infer specific intent to deceive (575 F.3d at 1327-29). Translated into a working checklist, a sufficient pleading must:

  • Name the specific individual associated with the patent's filing or prosecution who both knew of the material information and deliberately withheld or misrepresented it. A reference generally to a company's "agents and/or attorneys" is not enough (id. at 1329). You must name the inventor, the prosecuting attorney, or the in-house counsel, or at least allege facts identifying a specific person who owed the duty.
  • Plead facts showing that the specific individual knew of the withheld information -- not merely that the reference existed somewhere in the world. Knowledge of the prior art by someone at the company is insufficient; the pleading must connect knowledge to a person who bore the duty (id. at 1330).
  • Identify the specific claims and claim limitations to which the withheld reference is relevant, and identify where in that reference the material teaching is found. This is the materiality hook at the pleading stage. You must show the examiner cared about limitation X, and that the reference teaches X at column/line or page Y.
  • Plead facts explaining why deceptive intent is the reasonable inference. The pleader must allege underlying facts from which the court can infer that the individual made a deliberate decision to deceive (id. at 1328-31), not merely that an omission occurred.

A worked example helps. Suppose Acme Corp. sues Beacon Devices for infringing a patent on a temperature sensor. Beacon wants to plead inequitable conduct because Acme's own scientist, Dr. Reyes, presented a nearly identical sensor at a 2019 industry conference more than a year before Acme's filing date, and that disclosure was never cited to the examiner. A deficient pleading says: "Acme withheld the Reyes conference paper with intent to deceive." An Exergen-compliant pleading says, in substance: Dr. Reyes, a named inventor, personally authored and presented the 2019 conference paper, which disclosed [the specific sensor element claimed in limitation 1(b)] at slides 7-9; Dr. Reyes signed the inventor declaration acknowledging the duty of disclosure and was substantively involved in prosecution; Acme's prosecuting attorney, Ms. Lin, received a copy of the paper from Dr. Reyes on a specified date; neither cited it in any Information Disclosure Statement even after the examiner rejected the claims as obvious over a less relevant reference that the paper would plainly have anticipated; and the only reasonable inference from the timing, the personal authorship, and the targeted rejection is a deliberate decision to keep the paper from the examiner. That pleading names the who, pins the what and where, ties knowledge to a duty-bearer, hooks materiality to a specific limitation, and supplies an intent narrative. The motion to dismiss should fail.

A Wrinkle on the Intent Standard at the Pleading Stage

Courts are split on how much intent a pleading must show. Some demand that the complaint allege facts making deceptive intent the "single most reasonable inference" -- importing the Therasense proof standard into the pleading. Others adopt what they call the majority rule: at the pleading stage, a party need only allege facts from which the court can reasonably infer that the applicant made a deliberate decision to deceive, reserving the "single most reasonable inference" test for the merits (see BlackBerry Ltd. v. Typo Products LLC, 2014 WL 1867009, at *1-4 (N.D. Cal. May 8, 2014); ICM Controls Corp. v. Honeywell International, Inc., 2019 WL 7631075, at *13-14 (N.D.N.Y. Dec. 3, 2019) (noting the disagreement and adopting the majority rule)). Before you draft, read your district's and your judge's recent inequitable-conduct decisions; the difference can decide whether your pleading survives, and an over-cautious pleading wastes the diligence you put in beforehand.

Pleading the Cousins: Unclean Hands and Patent Misuse

Inequitable conduct often travels with two related equitable defenses, and their pleading standards depend on what they are based on.

Unclean hands is the older and broader doctrine -- the principle that a plaintiff seeking relief must come to court with clean hands (Keystone Driller Co. v. General Excavator Co., 290 U.S. 240, 245 (1933)). As a patent defense it generally requires (1) unconscionable conduct such as fraud, deceit, or bad faith, that (2) has an immediate and necessary relation to the matters at issue. Where an unclean-hands defense rests on the same facts as inequitable conduct, courts apply Rule 9(b)'s particularity standard and dismiss it if "egregious misconduct" -- such as falsifying or suppressing evidence -- is not pleaded with specifics (see Therasense, 649 F.3d at 1285-88; Collaboration Properties, Inc. v. Tandberg ASA, 2007 WL 205065, at *7 (N.D. Cal. Jan. 25, 2007); Human Genome Sciences, Inc. v. Genentech, Inc., 2011 WL 7461786, at *8 (C.D. Cal. Dec. 9, 2011)). Where unclean hands rests on litigation misconduct unrelated to prosecution, the more liberal Rule 8 notice-pleading standard governs (see Jazz Pharmaceuticals, Inc. v. Roxane Laboratories, Inc., 2013 WL 6858765, at *6 (D.N.J. Dec. 30, 2013)). Patent misuse follows the same logic: pled with Rule 9(b) particularity when grounded in fraud, and under Rule 8 otherwise.

One strategic note on unclean hands. Unlike inequitable conduct, litigation-based unclean hands ordinarily bars only recovery in the present suit, whereas prosecution-based fraud can render the patent unenforceable for all time. But the doctrine has real teeth: in Gilead Sciences, Inc. v. Merck & Co., 888 F.3d 1231 (Fed. Cir. 2018), the Federal Circuit affirmed the use of unclean hands to bar Merck from asserting its patents and to cancel a jury's substantial damages award based on pre-litigation and litigation misconduct. Unclean hands is a useful fallback precisely because its egregious-conduct focus sidesteps the but-for materiality the challenger must otherwise prove.

Step Two: Where to Dig -- The Evidence Map

The richest investigation begins before the complaint is even drafted, with publicly available records. Much of the strongest inequitable-conduct evidence is public, and the diligence you do here is what lets you plead with Exergen particularity. Below is a map of the sources, roughly in the order a litigator works them.

The Prosecution History (File Wrapper)

The complete prosecution history -- the "file wrapper" -- is the spine of any inequitable-conduct investigation, and it is public. Pull it directly from the USPTO's Patent Center / Image File Wrapper system for the asserted patent and for every related application. Read it cover to cover, chronologically, and build a timeline. You are reconstructing the conversation between the applicant and the examiner: every rejection, every amendment, every argument, every declaration, and every Information Disclosure Statement.

Two things to watch for. First, the basis of allowance. What argument or amendment finally persuaded the examiner to allow the claims? That is your materiality fulcrum. If the examiner allowed because the applicant argued that no prior art taught feature X, then a withheld reference that teaches feature X is your strongest candidate for but-for materiality. Second, the rejections that nearly succeeded. A reference that defeats a claim the applicant was struggling to save is far more likely to be but-for material than one cited in passing. The file wrapper, in short, tells you which omission would actually have mattered.

For the mechanics of how applicants traverse rejections in the first place -- the very documents you will be reading critically -- see our guide to Responding to Patent Office Actions -- Strategies for Overcoming Rejections, and for the obviousness arguments that so often turn on a single missing reference, Overcoming Obviousness Rejections -- A Comprehensive Guide to Section 103 Analysis.

Information Disclosure Statements (IDS)

The IDS is the formal vehicle by which an applicant tells the examiner what prior art it knows about. It is therefore both the place where the duty of disclosure is satisfied and the place where it is breached. The mechanics matter: applicants must file an IDS disclosing known material information within three months of filing or before the first office action on the merits (37 C.F.R. Section 1.97(b)), and supplemental IDSs are subject to escalating fee-and-certification requirements after the first office action, after final rejection, and after a notice of allowance (37 C.F.R. Section 1.97(c)-(e); MPEP Section 609.04(b)). Those certification points are gold for a litigator, because a late disclosure forces the applicant to certify when it actually learned of a reference -- and that representation can be tested against the record.

When you review the IDS history, ask:

  • Timing. When did the duty-bearer learn of a reference, and how long did it sit before disclosure -- if it was disclosed at all? A reference an inventor authored years before filing, never cited, is suspicious in a way that a reference disclosed promptly is not.
  • Selective disclosure and burial. Did the applicant cite a less-relevant reference while omitting a more-damaging one from the same family? Conversely, was a smoking-gun reference "buried" in an IDS listing hundreds of items so the examiner would never scrutinize it? Burial arguments are difficult after Therasense, because the act of disclosure usually defeats intent; but a pattern of burial combined with mischaracterization can still matter.
  • Cross-referencing related and foreign cases. This is the single most productive technique. Compare the IDS in the asserted U.S. patent against the prior art cited in (a) related U.S. applications (continuations, divisionals, continuations-in-part); (b) foreign counterpart applications; and (c) competitors' patents in the same field. References cited in one place and not another are leads. The duty expressly extends to art cited against related and foreign applications (MPEP Section 2001.06(a), (b)).
  • Quality of disclosure. For non-English references, was an accurate translation or an honest characterization provided? Submitting a misleading translation or characterizing a foreign-language reference inaccurately can rise to affirmative misrepresentation, independent of the underlying art's materiality.

A classic fact pattern: an examiner rejects the applicant's European counterpart over Reference A, but the applicant never brings Reference A to the U.S. examiner who is examining materially similar claims. Therasense itself arose from a related scenario, where representations made to the European Patent Office were inconsistent with -- and were not disclosed alongside -- representations made to the USPTO. For the disclosure regime in detail, the USPTO's duty-of-candor materials and MPEP Sections 2001-2005 are the authoritative reference.

Office Action Responses and Attorney Argument

Responses to rejections are where applicants characterize the prior art and their own invention, and characterizations can be misrepresentations. Material information is not limited to omitted references; it includes any statement inconsistent with a position the applicant takes in opposing a rejection (37 C.F.R. Section 1.56(b)(2)). Read every response asking:

  • Are references accurately described? Did the applicant tell the examiner that a reference "teaches away" from the invention or "does not disclose" element X when the reference plainly does? Mischaracterizing a reference of record can be affirmative misconduct even though the reference was technically disclosed (see Belcher Pharmaceuticals, LLC v. Hospira, Inc., 11 F.4th 1345, 1353-54 (Fed. Cir. 2021), where the patentee's representations to the FDA and the USPTO were fatally inconsistent).
  • Are experimental results complete and accurate? Arguments based on comparative data are a frequent source of trouble. Selectively reporting favorable data, comparing the invention against a strawman rather than the closest prior art, or presenting "prophetic" examples as if they were actual results are recurring fact patterns -- particularly in pharmaceutical and chemical cases (see Purdue Pharma L.P. v. Endo Pharmaceuticals Inc., 438 F.3d 1123, 1131 (Fed. Cir. 2006); Novo Nordisk Pharmaceuticals, Inc. v. Bio-Technology General Corp., 424 F.3d 1347, 1362 (Fed. Cir. 2005)).
  • Are positions consistent across the family and across jurisdictions? An applicant who tells the USPTO that a feature is critical and nonobvious while telling a foreign office, a later U.S. examiner, the FDA, or an investor that the same feature is routine has created an inconsistency you can exploit.

Inventor Declarations and Rule 1.131/1.132 Affidavits

Sworn declarations are gold because they must be truthful and because a false one triggers the affirmative-egregious-misconduct exception, sparing you the but-for materiality burden (Therasense, 649 F.3d at 1292; Intellect Wireless, 732 F.3d at 1344). In Intellect Wireless, the inventor filed a declaration falsely implying an actual reduction to practice, and a half-hearted later "correction" did not cure the defect -- the patent fell. Scrutinize:

  • Rule 1.131 declarations (sworn to "swear behind" a reference by proving an earlier invention date in pre-AIA cases). Do lab notebooks, emails, and witness testimony actually support the claimed conception and diligence? A Rule 1.131 declaration unsupported by contemporaneous records is a prime target, because the inventor's own testimony must be corroborated to carry weight (Schumer v. Laboratory Computer Systems, Inc., 308 F.3d 1304, 1316 (Fed. Cir. 2002)).
  • Rule 1.132 declarations (offered to rebut a rejection, often with data on unexpected results or commercial success). Is the data real, complete, and fairly presented? A declaration that overstates results or omits unfavorable comparisons is the kind of affirmative misconduct courts treat most harshly.
  • Inventorship declarations. Do the named inventors match the actual contributors reflected in invention-disclosure records and notebooks? Misjoinder or nonjoinder of inventors can be material (see Perceptive Biosystems, Inc. v. Pharmacia Biotech, Inc., 225 F.3d 1315, 1322 (Fed. Cir. 2000)) -- though, as always, it must be tied to deceptive intent rather than honest error to support inequitable conduct.

For the records that should underpin honest declarations in the first place, see How to Prepare an Invention Disclosure for Your Patent Attorney.

The Specification and Claims Compared Against the Outside World

Compare what the patent says against what the inventors said elsewhere: their own scientific publications, conference papers, marketing materials, product manuals, SEC filings, grant applications, and prior patents. A specification that touts a problem as "long unsolved" while the inventor's own published paper describes a prior solution is a contradiction worth running down. So is a written-description story that conflicts with the company's contemporaneous product literature, or a "best mode" the inventors plainly knew but did not disclose -- though note that a best-mode failure alone cannot render a patent unenforceable post-AIA (35 U.S.C. Sections 112, 282(b)(3)(A)). The point is contradiction: external statements that cannot be squared with the representations made to the examiner.

Assignment and Chain-of-Title Records

Assignment records, also public through the USPTO Assignment Database, can expose hidden relationships: a corporate affiliation with the author of a cited (or uncited) reference, an obligation to a third party, or a chain-of-title gap that undercuts a priority claim. Assignment timing that conflicts with claimed conception or reduction-to-practice dates can support an inference that a declaration overstated the inventive contribution or the invention date.

Related, Foreign, and Post-Grant Proceedings

Foreign counterparts and post-grant proceedings are comparison engines:

  • Foreign search reports and prosecution. Foreign patent offices often conduct independent searches and cite art the U.S. examiner never saw. Compare the references and, critically, compare the arguments. An applicant who characterizes the invention one way to the EPO and the opposite way to the USPTO -- without disclosing the inconsistency -- has handed you a Therasense-style claim.
  • Reexamination and PTAB proceedings. Inter partes review (IPR), post-grant review (PGR), and ex parte reexamination surface new prior art and force the patentee to take positions on validity. Those positions can be compared against prosecution-era representations. For an orientation to these proceedings, see Responding to Patent Office Actions -- Strategies for Overcoming Rejections.
  • Prior litigation. Earlier suits on the same or related patents may have generated discovery, expert reports, and deposition testimony that you can mine -- subject to protective-order constraints. Beware, too, that litigation misconduct in a parallel or prior case can itself feed an adverse inference of deceptive intent (Regeneron Pharmaceuticals, Inc. v. Merus N.V., 864 F.3d 1343, 1351, 1364 (Fed. Cir. 2017)).

Pre-Filing Internal Documents

Finally, the documents that predate filing -- lab notebooks, design records, internal emails, competitive-analysis memos, board presentations -- are where intent often lives. These are not public; they are the prize of discovery, discussed next. But your public-records investigation should be precise enough that your discovery requests can target them surgically rather than fishing.

Step Three: Discovery Strategy

Once you have pleaded inequitable conduct adequately, discovery is where you convert leads into clear-and-convincing proof. Inequitable conduct discovery is targeted, document-heavy, and witness-focused. For the broader mechanics, our general resource A Practical Discovery Refresher -- Mastering the Tools, Rules, and Pitfalls of Federal Civil Litigation is a useful backdrop.

A threshold point about local patent rules. In jurisdictions that have adopted them (the Northern District of California, the District of Delaware, the Western and Eastern Districts of Texas, and others), the accused infringer is often required to disclose the factual bases for its unenforceability defenses on a fixed schedule -- frequently within a month or two of the Rule 16 scheduling conference, alongside its invalidity contentions (see, e.g., N.D. Ill. LPR 2.3). Those contentions can be hard to amend later without a showing of diligence and good cause, so the accused infringer must front-load its theory. The patentee, for its part, should serve a contention interrogatory seeking "all bases" for the defense even where local rules already require disclosure, because theories evolve and the duty to supplement runs throughout the case.

Document Requests

Tailor your requests for production to the specific allegations you pleaded. Productive categories include: all documents concerning the prior art at issue, including when and how each duty-bearer learned of it; all communications between the inventors and prosecution counsel concerning the asserted patent and related applications; the complete files of foreign counsel handling counterpart applications; invention-disclosure forms, lab notebooks, and conception/reduction-to-practice records; documents concerning the decision to seek patent protection and the identification of named inventors; and any pre-suit opinions of counsel that touch on enforceability, validity, or the prior art.

A point lawyers sometimes get wrong: do not avoid requesting documents merely because they are likely privileged. Request them, and insist that responsive but withheld documents appear on a privilege log. The log itself -- dates, authors, recipients, and subject-matter descriptions -- frequently reveals the existence and timing of communications about the very prior art at issue, which can both support your intent narrative and lay the groundwork for a crime-fraud challenge (below). For the framework, see Mastering Document Discovery -- A Comprehensive Guide to Objecting and Responding to Requests for Production.

Interrogatories

Interrogatories pin the patentee to positions and force disclosure of the factual bases for its denials. From the patentee's side, an early contention interrogatory asking the accused infringer to state "all bases" for its inequitable-conduct defense is standard, and it can box in a defendant that pleaded thinly. From the accused infringer's side, interrogatories can ask the patentee to identify everyone involved in prosecuting the asserted and related patents and their roles, to identify each inventor's inventive contribution, to identify when each duty-bearer first learned of each reference, who decided what to disclose, and the patentee's contention as to why each omission was not material. Draft them with the Exergen elements in mind so the answers map onto your proof. See Mastering Interrogatories -- A Comprehensive Guide to Objecting and Responding in Civil Litigation.

Requests for Admission

You cannot use requests for admission (RFAs) to resolve the ultimate legal question of unenforceability, but you can use them to lock down the building blocks: that a particular individual was substantively involved in prosecution, that the individual received a particular reference on a particular date, that the reference was never cited in any IDS, that the reference discloses a particular element. Each admission removes a fact you would otherwise have to prove and narrows trial. See Strategic Responses to Requests for Admission -- A Comprehensive Guide for Legal Practitioners.

Depositions

Depositions are where intent is made or unmade. The essential witnesses are the named inventors and the prosecuting attorney (or patent agent). The accused infringer typically deposes them on conception, reduction to practice, the contribution of each inventor, knowledge of the prior art, the IDS process, and the basis for each declaration. A Rule 30(b)(6) notice can compel the patentee to designate a corporate witness on prosecution topics, including the decision to seek protection and the identification of inventors.

Two practical realities. First, the inventor and the prosecuting attorney are frequently not current employees of the patent owner, especially years after issuance. To reach them you will need third-party subpoenas under Rule 45 for documents and testimony. Plan for this early, because locating a retired prosecution attorney or a departed inventor takes time -- and a former prosecutor's recollection is often the hinge of the intent case. Second, the prosecuting attorney's deposition is fraught with privilege issues, examined below; prepare your crime-fraud theory before you take it, because you will want a clear record of the questions the witness refused to answer on privilege grounds. For deposition craft generally, see The Art and Science of Depositions in Federal Civil Litigation -- A Comprehensive Guide and, for the defending side, The Art of Defending Depositions in Federal Court -- A Comprehensive Guide.

Step Four: Privilege, the Crime-Fraud Exception, and Prosecution Bars

No area of inequitable-conduct practice generates more procedural fighting than privilege. Three issues recur.

The Attorney-Client Privilege Wall

Communications between the inventors and prosecution counsel are ordinarily privileged, and that privilege is the patentee's shield over exactly the documents you most want -- the candid discussions of what art existed and whether to disclose it. The patentee will assert privilege aggressively. Your tools are the privilege log, targeted depositions about non-privileged facts (privilege protects communications, not the underlying facts a witness knows), and, where warranted, a crime-fraud motion. For the doctrinal terrain, see A Comprehensive Guide to Federal Civil Litigation for Small Businesses, which surveys privilege and work-product basics.

The Crime-Fraud Exception

The attorney-client privilege does not protect communications made in furtherance of a crime or fraud. Because inequitable conduct sounds in fraud on the USPTO, a sufficiently supported showing can trigger the crime-fraud exception and pierce the privilege over the prosecution communications; indeed, a successful inequitable-conduct case can itself result in a finding of crime-fraud waiver (Therasense, 649 F.3d at 1289). The strategic sequence matters: you generally must make a prima facie showing of fraud -- often using the public file history and any non-privileged documents -- before a court will order in camera review or production of the privileged materials. In other words, you bootstrap. The public record gets you a threshold showing; the threshold showing gets you the privileged record; the privileged record (you hope) supplies the smoking-gun intent evidence.

Note the downstream leverage, too. A finding of inequitable conduct can support an "exceptional case" finding and an award of attorney's fees under 35 U.S.C. Section 285, and it can feed a Walker Process antitrust theory where fraud on the PTO is paired with anticompetitive enforcement of the resulting patent (see Walker Process Equipment, Inc. v. Food Machinery & Chemical Corp., 382 U.S. 172 (1965); TransWeb, 812 F.3d at 1306-09 (affirming antitrust liability and a treble-damages award including attorney's fees as antitrust damages)). The privilege fight, in short, is rarely just about a few emails; it is about the whole architecture of remedies that can follow a finding of fraud.

Prosecution Bars in the Protective Order

A prosecution bar is a provision in the litigation protective order that prevents lawyers who receive an opponent's highly confidential technical information from later participating in patent prosecution on related subject matter, lest they consciously or unconsciously misuse the information to shape claims. Prosecution bars cut both ways in inequitable-conduct litigation. They are negotiated at the outset of the case and can restrict which of your lawyers may both litigate the inequitable-conduct defense and advise on related prosecution or post-grant proceedings, such as a parallel IPR or a supplemental examination. Map your team's roles against any proposed bar before you agree to it; an overbroad bar can obstruct the coordination between your litigation and post-grant strategies. Be alert, too, that the patentee may seek supplemental examination under 35 U.S.C. Section 257 specifically to immunize the patent (discussed below), which can intersect with bar provisions governing who may appear before the USPTO.

Step Five: Proving Materiality

With evidence in hand, you must satisfy two distinct merits burdens. Start with materiality.

The But-For Test and the Examiner's Standard

After Therasense, materiality is ordinarily but-for: the withheld or misrepresented information must be one that the USPTO would not have allowed the claim over, had it known (649 F.3d at 1291). Crucially, materiality is judged from the examiner's vantage point during examination, not from a district court's invalidity vantage point. That distinction has real consequences for your burden of proof. To decide but-for materiality, the court asks what the PTO would have done, applying the PTO's examination standards -- the broadest reasonable interpretation of the claims (rather than the narrower Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005) (en banc), construction used at trial) and a preponderance of the evidence standard for unpatentability (rather than the clear-and-convincing standard required to invalidate an issued claim).

The upshot is counterintuitive but important: a reference can be material to inequitable conduct even if it would not invalidate the patent at trial (see American Calcar, Inc. v. American Honda Motor Co., 768 F.3d 1185, 1189 (Fed. Cir. 2014)). Because the PTO's bar for refusing a claim is lower than a court's bar for invalidating one, a withheld reference may have changed the PTO's decision even though it would not survive the clear-and-convincing invalidity gauntlet. By the same token, references that are merely cumulative of art already before the examiner are not material, no matter how relevant they look in isolation (Star Scientific, Inc. v. R.J. Reynolds Tobacco Co., 537 F.3d 1357, 1367 (Fed. Cir. 2008)). The cumulativeness question is therefore the central materiality battleground: the challenger argues the withheld art added something the examiner never had; the patentee argues it added nothing the examiner had not already weighed.

Materiality for Non-Prior-Art Conduct

Where the alleged misconduct is not withheld prior art -- for example, a false declaration or a mischaracterized data set -- courts focus on the misrepresentation itself, and a deliberately false affidavit relieves you of proving but-for materiality altogether under the egregious-misconduct exception (Therasense, 649 F.3d at 1292). That is one more reason false declarations and affirmatively false statements are the most efficient theory to pursue when the facts permit: they collapse the two-part proof into a single, document-anchored showing.

How Materiality Is Proved

Concretely, you prove materiality by reconstructing the examination. Show the examiner's reasoning at the point of allowance; show that the withheld reference teaches the very limitation the examiner found missing from the cited art; show that it is not cumulative of what the examiner already had; and show, often through a technical expert, that under the PTO's broadest-reasonable-interpretation and preponderance standards the examiner would not have allowed the claim with the reference in front of her. The closer the reference is to the claimed subject matter, and the more directly it answers the argument that won allowance, the stronger your materiality showing.

A worked example: recall Acme's temperature sensor. At prosecution, the examiner rejected claim 1 as obvious, the applicant amended to add limitation 1(b) (a specific calibration step), and argued no prior art disclosed it, after which the examiner allowed. The withheld Reyes conference paper discloses exactly that calibration step at slides 7-9, and it is not cumulative of anything in the cited art. Under the PTO's standards, the examiner almost certainly would not have allowed claim 1 over the Reyes paper. That is but-for materiality, proved by tying the reference's teaching to the limitation that won the case.

Step Six: Proving Intent to Deceive

Materiality is the easier element to prove. Intent is where most inequitable-conduct cases live and die.

The Single-Most-Reasonable-Inference Rule

Specific intent to deceive must be proved separately, and it cannot be inferred merely from materiality. The challenger must show that the duty-bearer knew of the information, knew it was material, and made a deliberate decision to withhold or misrepresent it (Therasense, 649 F.3d at 1290; see GS Cleantech Corp. v. Adkins Energy LLC, 951 F.3d 1310, 1324 (Fed. Cir. 2020)). Because direct evidence is rare, intent may be inferred from circumstantial evidence -- but the deceptive-intent inference "must be the single most reasonable inference able to be drawn from the evidence" (Therasense, 649 F.3d at 1290; Ohio Willow Wood, 735 F.3d at 1351). If an innocent inference is equally reasonable, you lose. Negligence -- even gross negligence -- and a merely "suspicious" omission do not suffice.

This is a high wall, and it is why the strongest cases combine several mutually reinforcing facts. A single uncited reference, standing alone, rarely supports deceit -- oversight is an equally reasonable inference. But assemble (1) that the inventor personally authored the reference; (2) that the reference was the closest art and answered the exact rejection the applicant was fighting; (3) that the applicant cited other, less relevant art while omitting this one; (4) a pattern of similar omissions across the family; and (5) the absence of any credible good-faith explanation -- and now deceit may become the single most reasonable inference. Intent is built from a constellation, not a single star.

There is one important escape hatch from the otherwise unforgiving intent standard. In Regeneron Pharmaceuticals, Inc. v. Merus N.V., 864 F.3d 1343, 1351, 1364 (Fed. Cir. 2017), the Federal Circuit affirmed an adverse inference of specific intent to deceive drawn from the patentee's litigation misconduct -- discovery abuses that obscured the prosecution facts. The lesson cuts both ways: a patentee that stonewalls or spoliates during the inequitable-conduct fight can hand the challenger the very intent finding the merits would not otherwise support, and a challenger should preserve and document any such misconduct meticulously.

The Good-Faith-Explanation Asymmetry

A useful asymmetry: the patentee need not offer a good-faith explanation for its conduct unless and until the challenger has shown a threshold level of deceptive intent (Therasense, 649 F.3d at 1291). Practically, this means your job in discovery and at trial is to push the evidence past that threshold. Once you do, the silence -- or the implausibility of any innocent story -- begins to work for you. Conversely, if you represent the patentee, supplying a credible, contemporaneous good-faith explanation (for example, a reasoned judgment that the reference was cumulative of art already of record) is often the most effective defense, because it supplies the competing reasonable inference that defeats the "single most reasonable inference" test.

Knowledge of Materiality, Not Just Existence

Note the precision of the Exergen/Therasense knowledge requirement. It is not enough that the duty-bearer knew the reference existed; the challenger must show the duty-bearer knew the reference was material and then deliberately decided to withhold it. Discovery should therefore target what the individual understood about the reference's significance: did they read it, summarize it, flag it internally as a problem, or discuss it with counsel? Internal documents that show the duty-bearer recognized the reference's relevance are far more probative than documents showing mere awareness of its existence. A scientist's email calling a competitor's paper "exactly what the examiner is worried about" is worth a hundred references buried in a literature folder.

Step Seven: Using Experts

Inequitable conduct is fact-intensive and technical, and experts are usually essential -- but the case law polices their lane carefully.

Technical Experts

A technical expert ordinarily testifies on whether a person of ordinary skill in the art would have considered the withheld information material -- that is, whether the examiner would have regarded it as important to patentability, whether it discloses the claimed limitations, and whether it is cumulative of the cited art. This testimony is the backbone of the materiality case. The boundary is the ultimate legal conclusion: courts exclude expert testimony that the patentee engaged in inequitable conduct, because unenforceability is a determination for the court, not the witness. Keep your technical expert on materiality and disclosure; do not let her wander into intent or the ultimate verdict. For how technical experts are deployed in adjacent invalidity work, see Overcoming Obviousness Rejections -- A Comprehensive Guide to Section 103 Analysis, which addresses the same person-of-ordinary-skill framework from the patentee's side.

Patent-Practice (PTO Procedure) Experts

You may also consider a patent-law/PTO-practice expert -- often a former examiner or experienced practitioner -- to explain the USPTO's practices, policies, and procedures: how examination works, what an IDS is supposed to do, what the duty of disclosure requires, and how an examiner would have treated a given reference. Courts are wary here. They typically will not let such an expert testify to legal conclusions or to the ultimate question of inequitable conduct, but they may permit testimony about PTO practice and procedure. Some courts decline to allow this kind of testimony at all, so check your jurisdiction and frame the expert's disclosure to stay within the permissible procedural-practice lane rather than drifting into legal opinion.

A Note on Corroboration

Where the patentee relies on the inventor's or prosecuting attorney's own testimony to establish good faith -- or where the inventor's account of conception underpins a Rule 1.131 showing -- that interested-witness testimony must be corroborated (Schumer v. Laboratory Computer Systems, Inc., 308 F.3d 1304, 1316 (Fed. Cir. 2002)). Courts assess corroboration under a "rule of reason," considering contemporaneous documents, physical evidence, circumstantial evidence about the inventive process, and the testimony of non-inventors (Sandt Technology, Ltd. v. Resco Metal & Plastics Corp., 264 F.3d 1344, 1350-51 (Fed. Cir. 2001)). For the challenger, the absence of corroboration is itself a line of attack.

Step Eight: Dispositive Motions and Trial

Summary Judgment Is Hard -- in Both Directions

Because materiality and intent are fact-intensive, summary judgment of inequitable conduct is rare (see Leviton Manufacturing Co. v. Universal Security Instruments, Inc., 606 F.3d 1353, 1363 (Fed. Cir. 2010)). A patentee can usually defeat the challenger's summary-judgment motion simply by pointing to record evidence permitting a reasonable inference of good faith. By the same token, summary judgment of no inequitable conduct is more attainable for the patentee when the record lacks evidence of materiality or intent -- which is one reason patentees move early and often to test the sufficiency of the defense, both on the pleadings and at summary judgment.

The Clear-and-Convincing Burden and the Trial Itself

At trial, the challenger must prove inequitable conduct by clear and convincing evidence (see In re Rosuvastatin Calcium Patent Litigation, 703 F.3d 511, 519 (Fed. Cir. 2012)) -- an exacting standard meaning the trier of fact must reach a firm conviction that the allegation is highly probable, well above the preponderance standard used in ordinary civil claims. Hold this distinct from the internal materiality sub-question, which the court answers under a preponderance standard because it is reconstructing a PTO decision; the ultimate defense still must be established clearly and convincingly.

The proof typically unfolds like this. The challenger calls a technical expert on materiality, possibly a PTO-practice expert on procedure, and then examines (or cross-examines) the inventor and the prosecuting attorney to build intent. The patentee answers with its own experts and with the inventor's and attorney's good-faith testimony (corroborated, where required). Inequitable conduct is generally tried to the bench, not a jury, because it is equitable in nature -- though courts may use an advisory jury under Rule 39 or try the issue by the parties' consent.

Trial structure matters too. Courts commonly bifurcate inequitable conduct from infringement and validity under Rule 42(b), and they have wide discretion to try it before, after, or alongside the jury phase -- sometimes even after appeal of the other issues (see, e.g., Ductmate Industries, Inc. v. Famous Distributing, Inc., 2014 WL 4104810, at *5-8 (W.D. Pa. Aug. 19, 2014)). Confer with local counsel and study your judge's practice; the sequencing can affect everything from your witness order to your settlement leverage. On appeal, the Federal Circuit reviews the ultimate inequitable-conduct determination for abuse of discretion, but reviews the underlying materiality and intent findings for clear error because they are factual (American Calcar, 768 F.3d at 1189).

Defending the Patent Owner

This article is a litigator's companion for both sides. If you represent the patentee, the same map tells you where the attack will come from -- and how to prepare. The best of these defenses are prophylactic, built into prosecution long before any complaint is filed.

Build a clean prosecution record from the start. The single best defense is a record that makes deceit implausible. During prosecution, disclose generously, characterize prior art accurately, support every declaration with contemporaneous records, present prophetic examples as prophetic (never in the past tense), and document the reasons for disclosure decisions. A contemporaneous note that a reference was judged cumulative of art already of record is powerful evidence of good faith years later. Remind the client of the ongoing duty of candor in every written communication, request prior art at each stage, and file timely IDSs (37 C.F.R. Section 1.97). The disclosure habits that prevent inequitable conduct are the same ones described in How to Prepare an Invention Disclosure for Your Patent Attorney and Responding to Patent Office Actions -- Strategies for Overcoming Rejections.

Attack the pleading first. Move to dismiss or strike under Exergen and Rule 9(b). Many inequitable-conduct defenses are pleaded on suspicion and cannot name the who, tie knowledge to a duty-bearer, or hook materiality to a specific limitation. The pleading stage is your cheapest and often best off-ramp.

Supply the competing inference. Because the challenger must make deceit the single most reasonable inference, your defense is to make innocence a reasonable inference. A credible good-faith explanation -- oversight, a reasonable materiality judgment, reliance on counsel, cumulativeness under Star Scientific -- defeats the defense even if the underlying omission is conceded.

Do not commit litigation misconduct. Regeneron is the cautionary tale. A patentee that obstructs discovery into the prosecution facts risks an adverse inference of the very intent it is trying to disprove. Litigate the defense cleanly.

Consider supplemental examination -- carefully and early. Section 257 of the AIA (35 U.S.C. Section 257) lets a patent owner ask the USPTO to consider, reconsider, or correct information believed relevant to the patent. If the information is considered during supplemental examination, the patent cannot later be held unenforceable on the basis of that information. Supplemental examination is thus a potential cure for a known prosecution defect -- but it must be requested before litigation triggers the statute's exclusions, and the request itself can alert adversaries to a problem they had not spotted. Time it deliberately, and coordinate it with any prosecution-bar provisions in pending litigation.

Mind the downstream consequences. A patentee who loses on inequitable conduct faces more than an unenforceable patent. The doctrine of infectious unenforceability can spread the defect to related patents and applications in the family (Therasense, 649 F.3d at 1288-89; Consolidated Aluminum Corp. v. Foseco International Ltd., 910 F.2d 804, 808-12 (Fed. Cir. 1990); see Guardant Health, Inc. v. Foundation Medicine, Inc., 2020 WL 2477522, at *5 (D. Del. Jan. 7, 2020)). A finding can also support an exceptional-case fee award under 35 U.S.C. Section 285, a crime-fraud waiver of privilege, and Walker Process antitrust exposure with treble damages. Note the contrast with ordinary invalidity, which is claim-specific under 35 U.S.C. Section 288: inequitable conduct as to a single claim taints the whole patent. The asymmetry of the stakes is precisely why candor during prosecution is non-negotiable. For the patent owner's broader litigation playbook, see Comprehensive Guide to Patent Infringement Litigation -- From Summary Judgment Denial to Post-Trial.

Putting It Together: A Worked Investigation

Return one last time to Acme Corp. v. Beacon Devices. Here is how the whole sequence looks in practice. (The companies and facts are invented; the legal moves are real.)

Beacon's litigation team begins, before answering, by pulling the complete file wrapper for Acme's patent and its two continuations. The timeline shows the examiner allowed claim 1 only after Acme added the calibration limitation 1(b) and argued no prior art taught it. A parallel review of the inventors' publications turns up Dr. Reyes's 2019 conference paper, which discloses that exact calibration step. A check of the foreign counterpart reveals the EPO cited the Reyes paper against Acme's European claims -- yet the U.S. file wrapper shows it was never listed in any IDS. Assignment records confirm Dr. Reyes was a named inventor and Acme employee throughout.

That public-record work supports an Exergen-compliant pleading: it names Dr. Reyes (and prosecuting attorney Ms. Lin), shows knowledge (Reyes authored the paper; the EPO cited it), hooks materiality to limitation 1(b), shows the paper is not cumulative of the cited art, and supplies an intent narrative (personal authorship, omission while citing weaker art, the targeted rejection). Acme's motion to dismiss under Rule 9(b) fails.

In discovery, Beacon serves document requests for all communications about the Reyes paper, the foreign-counsel file, and invention records; it serves interrogatories asking when each duty-bearer learned of the paper and Acme's contention on materiality and cumulativeness; and it notices the depositions of Reyes and Lin, with a Rule 45 subpoena to Lin's former firm. The privilege log lists an email from Reyes to Lin, dated shortly after the EPO citation, subject "re: conference paper / EP rejection." Beacon makes a prima facie crime-fraud showing on the public record and the log, and the court orders in camera review. The email shows Reyes and Lin discussed the paper and decided not to cite it because it was "too close." That is the intent evidence -- knowledge of materiality plus a deliberate decision to withhold.

At trial, Beacon's technical expert testifies that under the PTO's broadest-reasonable-interpretation and preponderance standards the examiner would not have allowed claim 1 over the Reyes paper, and that the paper is not cumulative (materiality). A PTO-practice expert explains the IDS duty and how an examiner would have treated the reference (procedure). Beacon examines Reyes and Lin on the "too close" email (intent). On this record, deceit is the single most reasonable inference, materiality is established, and the court -- sitting in equity, after bifurcation under Rule 42(b) -- holds the patent unenforceable. The continuations, prosecuted on the same omission, fall under infectious unenforceability, and the court flags the matter as a candidate for an exceptional-case fee award.

The example is invented, but every move in it tracks the law described above. That is the point: inequitable conduct is won not by a single dramatic document but by methodical reconstruction of the prosecution, disciplined discovery, careful expert work, and a relentless focus on making deceit the only sensible explanation.

Key Takeaways

  • Inequitable conduct can render an entire patent -- and, through infectious unenforceability, related patents -- unenforceable, so the stakes dwarf ordinary invalidity, which is claim-specific under 35 U.S.C. Section 288.
  • The duty of candor (37 C.F.R. Section 1.56) binds every inventor, prosecuting attorney or agent, and anyone substantively involved, and persists through allowance. It is enforced almost entirely through the litigation defense, not by the USPTO.
  • You must plead the defense with Rule 9(b) particularity under Exergen: name the specific duty-bearer, show that person's knowledge of the material information, hook the omission to specific claims and limitations, and supply facts supporting a deliberate decision to deceive.
  • Therasense requires two independent elements -- but-for materiality and specific intent to deceive -- each by clear and convincing evidence, with no sliding scale. The deceptive-intent inference must be the single most reasonable inference, and negligence is never enough.
  • Materiality is judged from the PTO's vantage point (broadest reasonable interpretation, preponderance), so a reference can be material even if it would not invalidate the patent at trial -- unless it is merely cumulative (Star Scientific). A deliberately false affidavit triggers the egregious-misconduct exception and excuses the but-for showing.
  • Most of the best evidence is public: file wrappers, IDS histories, foreign counterparts, inventor publications, and assignment records. Use the public record to plead with particularity and to bootstrap a crime-fraud showing.
  • Discovery is targeted: document requests aimed at the pleaded references, interrogatories that map to the Exergen elements, RFAs to lock down building blocks, and depositions of the inventor and prosecuting attorney (often via Rule 45 subpoena). Watch local-patent-rule contention deadlines.
  • Mind the privilege battles and downstream remedies: insist on a privilege log, build a crime-fraud theory, and remember that a finding can support Section 285 fees and Walker Process antitrust liability.
  • Use a technical expert on materiality and a PTO-practice expert on procedure, but keep both away from the ultimate legal conclusion, which belongs to the court; interested-witness testimony must be corroborated.
  • For patentees: a clean prosecution record, an early Exergen motion, a credible good-faith explanation, scrupulous litigation conduct (to avoid a Regeneron adverse inference), and -- where appropriate -- timely supplemental examination under 35 U.S.C. Section 257 are the core defenses.

Frequently Asked Questions

What is the difference between inequitable conduct and invalidity? Invalidity attacks particular claims under standards like novelty (35 U.S.C. Section 102) or non-obviousness (35 U.S.C. Section 103), and an invalid claim does not necessarily affect the rest of the patent (35 U.S.C. Section 288). Inequitable conduct is an equitable defense that, if proven against even one claim, renders the whole patent unenforceable and can spread to related patents through infectious unenforceability. The two also use different proof standards and viewpoints: materiality for inequitable conduct is judged from the PTO's examination perspective under a preponderance standard, so a reference can be material to inequitable conduct even though it would not invalidate the patent in court.

Who exactly owes the duty of candor? The duty runs individually to each prosecuting attorney or patent agent, to each named inventor (who acknowledges it in the inventor's declaration under 37 C.F.R. Section 1.63(c)), and to anyone associated with the inventor, attorney, agent, or assignee who is substantively involved in preparing or prosecuting the application -- including in-house counsel (37 C.F.R. Section 1.56(c); MPEP Section 2001.01). It lasts throughout prosecution, including after a notice of allowance.

How specific does an inequitable-conduct pleading have to be? Very. Under Exergen Corp. v. Wal-Mart Stores, Inc., 575 F.3d 1312 (Fed. Cir. 2009), and Rule 9(b), you must plead the "who, what, when, where, and how" of the misrepresentation or omission, name the specific individual who both knew the material information and withheld it, tie the withheld reference to specific claims and limitations (and to where in the reference the teaching appears), and allege facts supporting a deliberate intent to deceive. Generic references to a company's "agents and/or attorneys" are insufficient.

Can I prove inequitable conduct with only circumstantial evidence of intent? Yes -- direct evidence of intent is rare, and courts permit intent to be inferred from circumstantial evidence. But under Therasense, the inference of deceptive intent must be "the single most reasonable inference able to be drawn from the evidence." If an innocent explanation is equally reasonable, the defense fails, and negligence (even gross negligence) is not deceit. That is why strong cases stack multiple mutually reinforcing facts rather than relying on a single omission. In unusual cases, a court may also draw an adverse inference of intent from a patentee's litigation misconduct (Regeneron v. Merus).

Does the attorney-client privilege block me from the key documents? Often it shields the inventor-attorney communications you most want. But the privilege protects communications, not the underlying facts a witness knows, and the crime-fraud exception can pierce it where you make a prima facie showing of fraud on the PTO. The standard sequence is to use the public file history and any non-privileged materials to make that threshold showing, then move for in camera review and production of the privileged communications.

What is supplemental examination, and can it save a patent? Under 35 U.S.C. Section 257 (added by the America Invents Act), a patent owner can ask the USPTO to consider, reconsider, or correct information believed relevant to the patent. If the information is considered during supplemental examination, the patent cannot later be held unenforceable on the basis of that information. It is a potential cure for a known prosecution defect, but it must be pursued before litigation triggers the statute's exclusions, and the request can tip off adversaries, so timing is critical.

Is inequitable conduct decided by a jury? Usually not. Because it is equitable, inequitable conduct is generally tried to the judge, who makes findings on materiality and intent. Courts may use an advisory jury under Rule 39 or try the issue by the parties' consent, and they commonly bifurcate it from infringement and validity under Rule 42(b).

What happens to the patent owner if it loses? The asserted patent and all its claims become unenforceable; related patents may fall through infectious unenforceability; the case may be deemed "exceptional" for a fee award under 35 U.S.C. Section 285; privilege over prosecution communications may be waived under the crime-fraud exception; and, where the fraudulent patent was enforced anticompetitively, the patentee may face Walker Process antitrust liability with treble damages.

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This article is provided by mclaw.io for general informational purposes only and does not constitute legal advice. Inequitable conduct is a fact-intensive defense governed by rapidly evolving Federal Circuit precedent, and outcomes depend on the specific record in each case. Readers should consult qualified patent litigation counsel before acting on any matter discussed here.