The U.S. Supreme Court on May 28th unanimously vacated the Federal Circuit's landmark decision in Festo Corp. v. Shoketsu Kinzoku Kogyo K.K. Co., Ltd., rejecting the "literalism" of the lower court, which had imposed a "complete bar" against resort to the doctrine of equivalents where a patentee had amended his claims during prosecution.
The Supreme Court reaffirmed its "flexible" approach to the doctrine, but tightened the requirement placed on patent holders to "bear the burden of showing that the amendment does not surrender the particular equivalent in question." The Supreme Court agreed with the CAFC that amendments giving rise to estoppel are not limited to those which are intended to avoid the prior art, again placing the burden on the patentee to show that his amendments were not for purposes of patentability. Further contours of the law in this rapidly evolving area remain to be settled when the Federal Circuit revisits Festo pursuant to the Supreme Court's remand of the case.