Markush claim

In the US, claim language defined by a Markush grouping requires selection from a closed group "consisting of" the alternative members¹. Four practical points follow from the MPEP:

• A claim that lists alternatives to define a limitation is an acceptable claim construction, and should not necessarily be rejected as confusing under 35 U.S.C. 112(b) or as improper³.
• If a Markush grouping requires a material selected from an open list, for example a group "comprising" or "consisting essentially of" the alternatives, the claim should generally be rejected under 35 U.S.C. 112(b) as indefinite, because it is unclear what other alternatives are meant to be covered³.
• If the claim is meant to cover combinations or mixtures of the alternatives, it may say so, for example "at least one member" selected from the group or "or mixtures thereof"³.
• A long list is not necessarily indefinite, because breadth is not indefiniteness. A group can still be so expansive that persons skilled in the art cannot determine the metes and bounds of the claimed invention³.

A Markush claim may be rejected on "improper Markush grouping" principles if either the members do not share a single structural similarity or they do not share a common use¹. The members share a single structural similarity when they belong to the same recognized physical or chemical class or the same art-recognized class, and share a common use when they are disclosed in the specification or known in the art to be functionally equivalent in the context of the claimed invention¹.

Where the claim lists alternative chemical compounds that do not belong to a recognized class, the grouping may still be proper if they share a substantial structural feature that is essential to a common use. In In re Harnisch (CCPA 1980), the MPEP says the court found a group of coumarin derivatives proper because the compounds, viewed as wholes, all share a coumarin group and the property of being a dye¹.

A rejection for an improper Markush grouping is a rejection on the merits and may be appealed to the Patent Trial and Appeal Board¹. To overcome it, an applicant may set out each alternative, or each grouping of patentably indistinct alternatives, in a series of independent or dependent claims, or argue that the members in fact share a single structural similarity and a common use¹.

A Markush claim may include independent and distinct inventions, in which case the examiner may require the applicant to make a provisional election of a single species, or a grouping of patentably indistinct species, before examination on the merits². There is one exception: if the members of a proper Markush group are sufficiently few in number or so closely related that the entire claim can be searched and examined without serious burden, the examiner must examine all the members².

1. Provisional electionThe applicant's election is the starting point for the search and examination of the claim².
2. Examination of the elected speciesThe Markush claim is examined fully for the elected species, and further to the extent needed to determine patentability².
3. If the elected species is not allowableIf it is anticipated or rendered obvious, the Markush claim and the claims to the elected species are rejected, and claims to nonelected species are held withdrawn from further consideration².
4. If the elected species is allowableExamination of the Markush claim is extended. If prior art then anticipates or renders obvious the claim for a nonelected species, the Markush claim is rejected².

Where a claim reads on multiple species, only one species needs to be taught or suggested by the prior art for the claim to be anticipated or rendered obvious². See Prior art for what counts.