The Federal Circuit, describing the invocation of "inequitable conduct" as a "a significant litigation strategy", reigned in the standard to prove such an assertion in a split decision authored by Chief Judge Rader. Therasense, Inc. v. Becton, Dickinson and Co., 2011 U.S. App. LEXIS 10590, at *26 (Fed. Cir. May 25, 2011). In so doing, the Federal Circuit rejected the so-called "sliding scale", which

weaken[ed] the showing needed to establish inequitable conduct [by placing] intent and materiality together on a "sliding scale." This modification to the inequitable conduct doctrine held patents unenforceable based on a reduced showing of intent if the record contained a strong showing of materiality, and vice versa. In effect, this change conflated, and diluted, the standards for both intent and materiality. Id.

Instead, the Federal Circuit held that the standard for inequitable conduct is a "but for" test as to materiality. Id. at *37. Namely, the "prior art is but-for material if the PTO would not have allowed a claim had it been aware of the undisclosed prior art." Id. "In making this patentability determination, the court should apply the preponderance of the evidence standard and give claims their broadest reasonable construction." Id.

The second prong of inequitable conduct - intent - requires proof by clear and convincing evidence that the patentee intended to deceive the Patent Office. Neither negligence nor even gross negligence are sufficient to prove intent. Id. at *25. By reigning in the standard to prove inequitable conduct the court remedied what it described as "the way inequitable conduct has metastasized." Id. at *43. The Federal Circuit did leave open a possible exception to its new standard "[w]hen the patentee has engaged in affirmative acts of egregious misconduct, such as the filing of an unmistakably false affidavit, the misconduct is material." Id. at *39.