Sitting en banc last week, the U.S. Court of Appeals for the Federal Circuit stiffened the tests for claims of inequitable conduct. As Chief Judge Rader stated: “This court now tightens the standards for finding both intent and materiality in order to redirect a doctrine that has been overused to the detriment of the public.” In doing so, the Federal Circuit vacated a lower court finding of inequitable conduct, and called the inequitable conduct defense a “plague” not only on the courts but also the entire patent system.

The court clarified that, to satisfy the intent prong, a challenger must establish that “the applicant knew of the [prior art] reference, knew that it was material, and made a deliberate decision to withhold it.” With regard to the materiality prong, the majority adopted a “but for” standard, requiring the challenger to show that “the PTO would not have allowed a claim had it been aware of the undisclosed prior art.”

The majority did provide one exception to the “but for” standard; namely, for cases in which the patentee has engaged in egregious misconduct such as deliberately filing a false affidavit.

The case is Therasense Inc. v. Becton, Dickinson & Co., Fed. Cir., No. 2008-1511, 5/25/11, and the opinion is available at