Background
Larson Manufacturing held patents on storm door hinge assemblies and sued Aluminart for infringement. Aluminart counterclaimed that the patents were unenforceable due to inequitable conduct during prosecution — specifically, that Larson had failed to disclose material prior art to the Patent Office. The prior art at issue included a competitor’s product that a Larson employee had seen at a trade show and that closely resembled the claimed invention.
The district court found inequitable conduct on a relatively thin record of intent evidence and held the patents unenforceable. Larson appealed, arguing that the district court had not applied sufficiently demanding standards for either the materiality or intent elements of inequitable conduct — then a heavily litigated doctrine that critics argued was being asserted too broadly as a litigation tactic.
The Court’s Holding
The Federal Circuit vacated the inequitable conduct finding and remanded for further analysis. The court reaffirmed that inequitable conduct requires clear and convincing evidence of both: (1) material misrepresentation or omission — meaning information the examiner would have considered important in deciding patentability; and (2) subjective intent to deceive the Patent Office, not merely negligence or oversight. Both prongs must be independently established, and intent cannot simply be inferred from materiality alone.
The court also addressed the legal significance of an examiner’s independent awareness of withheld prior art. Even if the examiner independently knew of or found the same prior art that was withheld, that fact does not excuse the patentee’s duty of candor or eliminate materiality — because the duty of disclosure exists regardless of whether the omission actually misled the examiner. The purpose of the disclosure obligation is systemic: the PTO is entitled to full disclosure so that examination can proceed with complete information.
Key Takeaways
- Inequitable conduct requires clear and convincing evidence of both materiality and intent to deceive — each element must be independently proved and intent cannot be inferred solely from materiality.
- The fact that an examiner may have independently known of or discovered withheld prior art does not eliminate the duty to disclose that art or excuse the omission as immaterial.
- Courts must carefully assess the full record before finding intent to deceive — negligence, carelessness, or poor judgment during prosecution does not rise to the level of culpability required for inequitable conduct.
- Patent practitioners should disclose all known material prior art and should maintain detailed records of prosecution-era decisions regarding disclosure to rebut inequitable conduct claims in later litigation.
Why It Matters
Larson Manufacturing was part of a sustained Federal Circuit effort in the mid-2000s to tighten the inequitable conduct doctrine, which many practitioners and commentators had criticized as being asserted too routinely as a litigation weapon. The heightened standards for both materiality and intent articulated in cases like Larson contributed to the legal landscape that led the Federal Circuit to undertake a comprehensive reformation of the doctrine in Therasense, Inc. v. Becton, Dickinson (2011), which further tightened the but-for materiality and specific-intent-to-deceive requirements.
For patent prosecution attorneys, the case reinforced the practical importance of thorough prior art disclosure and contemporaneous documentation of disclosure decisions. For litigants, it established that courts cannot reach an inequitable conduct finding without carefully analyzing and weighing the full evidence on both intent and materiality — preventing inequitable conduct from functioning as an easily-asserted, hard-to-rebut invalidity theory.