On May 28, 2002, the Supreme Court vacated and remanded the U.S. Court of Appeals for the Federal Circuit's ("CAFC") decision in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 234 F.3d 558 (Fed. Cir. 2001), cert. granted, 533 U.S. 915. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 122 S. Ct. 1831 (2002). This much awaited decision revives the nearly lost doctrine of equivalents and has the patent bar breathing a collective sigh of relief. While the Supreme Court agreed with the CAFC's clarifications regarding what may constitute a narrowing amendment for purposes of triggering prosecution estoppel, the CAFC's choice of complete bar to equivalents for such amendments was not well received. The Supreme Court has returned the approach to the doctrine of equivalents to the status quo, resuscitating the flexible bar, and adding, arguably, a new twist of its own.
The CAFC's Decision. In the underlying decision, the CAFC held that all amendments made for reasons substantially related to patentability constitute prosecution history estoppel. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 234 F.3d 558, 566 (Fed. Cir. 2000), cert. granted, 533 U.S. 915 (2001). Prior to the CAFC's decision, it was unclear whether or not claim amendments made for reasons not directly related to overcoming prior art rejections, could create prosecution history estoppel. Such non-prior art rejections may include, inter alia, amendments made in response to rejections under 35 U.S.C. § 112 and voluntary amendments. The CAFC held that all amendments are presumed to be related to patentability, unless there is some other evidence rebutting this presumption in the prosecution history. All ambiguities are to be decided in favor of the public, i.e., are presumed to create estoppel, since the public has only the written prosecution record to rely on in making decisions regarding how to avoid infringement of the patented claims.
Even more far reaching, was the CAFC's bright-line holding that in such instances where an amendment creates estoppel, the estoppel constitutes a complete bar, wherein the amended claim element is entitled to no protection whatsoever under the doctrine of equivalents. Id. at 576.
The Supreme Court's Decision. The Supreme Court held that prosecution history estoppel may apply to any claim amendment made to satisfy the Patent Act's requirements, not just to amendments made to avoid the prior art, but estoppel need not bar suit against every equivalent to the amended claim element.