What is a Markush claim?

A Markush claim is a patent claim that sets forth a list of alternatives from which a selection is made; the listed alternatives form what practitioners call a Markush group or Markush grouping. The format is named after the appellant in Ex parte Markush, 1925 Dec. Comm'r Pat. 126, 127 (1924), the case in which the Commissioner of Patents accepted this grouped-alternative approach to claiming.

The standard language

Markush claims typically use the phrase "selected from the group consisting of" to introduce a closed set of alternatives; the "consisting of" language signals that only the explicitly listed members are covered and no unrecited alternatives may be substituted in.

A typical Markush element reads:

"...wherein R is selected from the group consisting of methyl, ethyl, and propyl."

The USPTO does not require this exact phrasing; alternatives expressed as "wherein R is methyl, ethyl, or propyl" receive the same examination treatment as the classic "selected from the group consisting of" formulation.

Where Markush claims are most used

Markush claims appear most frequently in metallurgy, chemistry, pharmacology, and biology, where a single claim can protect a family of structurally related compounds rather than requiring a separate claim for each variant.

Requirements: the two-part test

Not every list of alternatives qualifies as a valid Markush grouping. Under MPEP 2117, a proper Markush group must satisfy both of the following:

1. Single structural similarity. The members must share a single structural similarity, meaning they all belong to the same recognized physical, chemical, or art-recognized class. For processes or combinations, the members must be substitutable for one another with the expectation of achieving the same intended result.

2. Common use. The members must share a common use, meaning they are all functionally equivalent for the purpose served by that element in the claimed invention. Structural similarity alone is not enough. The grouped alternatives must genuinely perform the same role in the context of the claim.

When either condition fails, the grouping is improper. A Markush grouping is improper when either the members do not share a single structural similarity or they do not share a common use, and an examiner may reject such a claim on improper Markush grouping grounds. The typical response is to narrow the group, convert alternatives to separate dependent claims, or add specification language that explains the shared characteristic responsible for the common function.

Anticipation: the single-species rule

One of the sharpest practical risks in Markush claiming is how prior art destroys novelty. Under MPEP 2131.02, prior art that discloses a single species falling within the Markush group can anticipate the entire Markush claim, even if the reference does not mention every listed alternative.

To illustrate: if prior art discloses copper, a claim reciting "a metal selected from the group consisting of copper, silver, and gold" is anticipated in full; listing silver and gold alongside copper does not save the claim.

The practical lesson: search each individual alternative against the prior art before finalizing the Markush members.

Restriction requirements for diverse groups

A restriction requirement may be imposed on a Markush claim when the listed alternatives are so diverse that prior art invalidating the claim with respect to one member would not render the claim obvious with respect to the other members. This is the examiner's way of signaling that the claim effectively covers multiple distinct inventions.

When a restriction is imposed, the applicant provisionally elects one species or subgroup for initial examination; if that elected subject matter is found allowable, the examiner extends examination to the nonelected members before finally acting on the Markush claim as a whole.

Practical notes

• Identify the common characteristic in the specification. Explicitly state why all listed alternatives function the same way in your invention. This is the factual predicate that defeats an improper Markush rejection before the examiner ever raises it.
• Search every alternative before listing it. Because a single disclosed species in the prior art can anticipate the entire claim, prior art due diligence on each member is essential, not optional.
• Use "consisting of," not "comprising." A Markush group must be a closed group. Writing "selected from the group comprising A, B, and C" creates ambiguity about whether the list is open-ended; "consisting of" provides the clear boundary the format requires.
• Build in fallback sub-groups via dependent claims. If the broadest Markush claim is restricted or rejected, dependent claims reciting narrower sub-groups of the alternatives give you positions to argue without starting from scratch.