We discussed the Doctrine of Equivalents in a previous blog entry.  When might a patentee not have claim coverage extending to equivalents of elements in a patent claim?  In Festo Corp. v Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002), also known colloquially as Festo II, the Supreme Court vacated a previous ruling made by the Federal Circuit, and established important holdings regarding equivalents.  It was previously held that amending a patent application, to narrow a patent claim, gave rise to the presumption that equivalents to a particular claim element being amended were surrendered.  That is, amending a claim element to narrow the claim was presumed to constitute a surrender or giving up of equivalents to that claim element.  Equivalents to that claim element were no longer covered by the amended claim.  The newer ruling established that such amendments were no longer considered to create an absolute bar to equivalents.  Reasons for making the amendment could now be taken into account.  The presumption of surrender of equivalents still existed, but this presumption can be rebutted.  A showing that equivalents were not surrendered could now be considered.  Justice Kennedy delivered the majority opinion (separate excerpts below):

… when the court is unable to determine the purpose underlying a narrowing amendment--and hence a rationale for limiting the estoppel to the surrender of particular equivalents--the court should presume that the patentee surrendered all subject matter between the broader and the narrower language.

[In order to rebut this presumption] The patentee must show that at the time of the amendment one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent.