Lott & Fischer is an intellectual property law firm in Coral Gables, Florida. The firm concentrates its practice exclusively in intellectual property law, including U.S. and international patent, trademark, copyright, unfair competition, Internet, and entertainment law and related litigation.

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Resources > Articles > Checklist for Equitable Defenses in Patent Infringement Cases

By Leslie J. Lott, Esq.



• Material information withheld/or material false or misleading information disclosed [Rule 56 violation]

• Intent to deceive or mislead the examiner into granting a patent.

Practice Notes: Once the defendant establishes threshold levels of materiality and intent, court balances degree of materiality and intent to determine whether inequitable conduct occurred.J.P. Stevens & Co. v. Lex Tex Ltd., 747 F.2d 1553, 223 U.S.P.Q. 1089 (Fed. Cir. 1984).

Practice Notes: Inequitable conduct is essentially a claim of fraud, and must be plead with particularity in accordance with Rule 9(b) Fed.R.Civ.Pro. Advanced Cardiovascular Systems, Inc. v. Medtronic, Inc. 41 U.S.P.Q.2d 1770 (N.D. Calif. 1996)


• Unenforceability of all claims of all patents resulting directly or indirectly from conduct

• Award of attorney’s fees to prevailing defendant at court's discretion

• Possible antitrust liability

• Disciplinary action against attorneys or agents



• Unreasonable delay in filing suit (after plaintiff knew or should have known of claim)

• Material prejudice to the defendant

Practice Notes: Prejudice may be evidentiary or economic- evidentiary prejudice may be defendant’s inability to present adequate defense due to loss of records, death of witnesses, unreliability of memories of long past events; economic prejudice is due to loss of monetary investments or financial damage which likely would have been prevented by earlier suit. Wanlass v. General Electric Co., 46 U.S.P.Q.2d 1915 (Fed. Cir. 1998).

Practice Notes: Delay of more than 6 years gives rise to rebuttable presumption of laches.


• Bars recovery for conduct engaged in prior to suit

• Does not bar injunctive relief or recovery for activities conducted subsequent to filing suit



• Misleading statements or conduct

• Action in reliance

• Resulting prejudice

Practice Notes: Unlike laches, equitable estoppel does not involve a six year presumption. 6 Chisum, Patents §19.05[3].


• Bars recovery



• Position taken or representation made in prosecution

• Present inconsistent position as to claim construction

• Original position would defeat assertion of patent

PracticeNotes: File wrapper estoppel is actually not an affirmative defense, but a tool for construction of claims. 5 Chisum, Patents §18.05[1].It is a purely legal question for the court. Pharmacia & Upjohn Co. v. Mylan Pharmaceuticals, Inc., 46 U.S.P.Q.2d (Fed. Cir. 1998).

Practice Notes: Patentee may rebut presumption that limiting language was submitted for the purpose of obtaining patent. Warner Jenkinson Co. Inc. v. Hilton Davis Chemical Co., 117 S.Ct. 1040, 41 U.S.P.Q.2d 1865 (1997).


• Precludes claim construction which would resurrect subject matter surrendered during prosecution

• That which was given up in prosecution is not "equivalent" to that which is claimed