It appears that the en banc decision In re Donaldson of the Court of Appeals for the Federal Circuit (CAFC), will end the conflict between the Patent and Trademark Office (PTO) and the CAFC over the interpretation of "means or step plus function" language in claims during examination. 35 USC 112, paragraph 6 reads:

The PTO's view has traditionally been that during prosecution of an application "means plus function" claims should be construed broadly to cover all possible means for achieving the stated function. The reason given was that it was impossible for an examiner to determine what was or was not an "equivalent" of a feature described in the specification under examination. In considering questions of infringement, however, the courts have tried to give proper weight to the limitations set out in the statute on the manner in which such a claim is to be construed. In the Donaldson decision, the CAFC explicitly condemned the PTO's policy.

In reaching its decision, the CAFC analyzed the plain language of 35 USC 112, paragraph 6, and considered the language to be unambiguous and not supportive of the PTO's interpretation. The CAFC pointed out that paragraph 6 does not distinguish between patent prosecution in the PTO and enforcement in the courts and if Congress had intended this distinction it would have been included in the statute. The CAFC stated that the broadest reasonable interpretation that an examiner may give "means or step plus function" language is that statutorily mandated in 35 USC 112, paragraph 6 and therefore, the PTO may not disregard the structure disclosed in the specification corresponding to such language when rendering a patentability determination.

Following the Donaldson decision, the PTO issued guidelines stating that examiners shall interpret 35 USC 112, paragraph 6, "means or step plus function" language in a claim as limited to the corresponding structure, materials or acts described in the specification and equivalents thereof Pursuant to the guidelines the prior art element is not an equivalent unless it performs the identical function.

Under the guidelines, the examiner has the initial burden of proof for "showing that the prior art structure or step is the same as or equivalent to the structure, material, or acts described in the specification which has been identified as corresponding to the claimed means or step plus function." Then the burden is shifted to the applicant to show that "the element shown in the prior art is not an equivalent of the structure, material or acts disclosed in the application." It is also appropriate for the Examiner to cite the prior art if the claimed "means or step plus function" is obvious from the prior art.

The guidelines also provide that an Examiner may issue a rejection under 35 USC 112, paragraphs 1 (enablement, written description) and/or 2 (the claim is indefinite) if a "means or step plus function" limitation recited in a claim is not supported by corresponding structure, material or acts in the specification.