The issue on appeal in Hor v. Chu was whether the district court erred in finding that laches barred the plaintiffs' inventorship claims. Specifically, the issue of first impression is whether the laches period for a claim for correction of inventorship under Section 256 of the Patent Act (35 U.S.C. § 256) begins to accrue when the patent issues.

The court also decided whether the district court correctly:

The plaintiffs, Hor and Meng worked with the defendant, Chu, in the University of Houston physics research lab. The plaintiffs sued Chu in the US District Court for the Southern District of Texas for correction of inventorship of two US patents relating to superconducting compositions with transition temperatures higher than the boiling point of liquid nitrogen:

The '866 patent was filed on March 26, 1987 and issued on June 6, 2006. The '418 patent was filed on January 23, 1989 and issued on May 4, 2010. Hor filed suit in 2008 and Meng intervened in 2010.

Chu argued that the plantiffs' claims were barred by laches because the plaintiffs knew or should have known by as early as 1987 that they were not named inventors on both the '866 and '418 patent applications. The district court agreed with Chu and found that laches applies because:

The district court also entered judgment in Chu's favor on the plaintiffs' unclean hands defense. Alternatively, the district court sua sponte held that the inventorship claims were barred by equitable estoppel.

The plaintiffs then appealed to the US Court of Appeals for the Federal Circuit.

In its November 14, 2012 decision, the Federal Circuit:

For a successful laches defense, a defendant must show that:

For inventorship claims under Section 256 of the Patent Act (35 U.S.C. § 256), a delay of six years after a claim accrues creates a rebuttable presumption of laches. The district court held that the laches period began before the patent issued, finding that Chu's laches defense applied.

On appeal, the Federal Circuit clarified that the laches period begins when the patent issues. Since the '866 patent issued in 2006 and the '418 patent issued in 2010, Hor filing suit in 2008 was well within the six-year rebuttable presumption period for laches. The Federal Circuit also found that the statutory text of Section 256 supports its holding that the laches period begins when the patent issues.

The plaintiffs did not provide evidence to dispute the district court's finding that the unclean hands defense applied on appeal. The Federal Circuit did not disturb the district court's decision on this point.

The Federal Circuit vacated the district court's judgment in Chu's favor based on equitable estoppel because estoppel is an affirmative defense that must be pled. Chu did not assert equitable estoppel as an affirmative defense in his answer nor did he include it in his motion for summary judgment to the district court. Because Chu failed to properly plead the equitable estoppel defense, the Federal Circuit vacated this portion of the district court's judgment.

This case establishes that the clock for the laches period for inventorship claims starts when the patent issues. Counsel for parties asserting the laches defense in such claims should be mindful of when the patent actually issued.