Welcome to the new version of the Patents Manual. Please note there are changes to the numbering and sequence of the chapters and pages in the manual. You are encouraged to take the time to explore and familiarise yourself with this new structure. Markush Practice

Date Published

A Markush claim is a claim that defines alternatives.  Markush claims can be either chemical or non-chemical, provided they amount to a claim to alternatives [PCT/GL/ISPE/12 at para 10.17]. Thus, a claim to a list of compounds identified by name or a generic formula are equally regarded as Markush claims.

Paragraphs 10.28 to 10.33, 10.45 to 10.49, and 10.52 to 10.54 of the PCT International Search and Preliminary Examination Guidelines considers unity of invention and Markush claims and the practice described is illustrated in examples 8 to 13, 25 to 29, and 32 to 34.

For Markush claims, the requirement of a technical interrelationship and the same or corresponding special technical features, as defined in Rule 13.2, are to be considered to be met when the alternatives are of a similar nature.

When considering a Markush claim for chemical compounds, it is necessary for all alternatives to have a common activity or property.  In addition, it is only necessary for there to be a "significant structural element shared by all of the alternatives", to establish unity of invention.  (The important thing to note is that it is not necessary for this "significant structural element" to be novel).

When determining whether there is a common property shared by the alternatives, the property should be defined sufficiently broadly that all of the claimed members possess the property.  If the property is defined too narrowly, then the claim will inevitably lack unity.

Examples 8 to 13, 25 to 29, 32 to 34 in paragraphs 10.28 to 10.33, 10.45 to 10.49, and 10.52 to 10.54 of the PCT International Search and Preliminary Examination Guidelines provide some assistance in determining if a common "significant structural element" exists for a chemical structure containing alternatives.

In determining unity of invention for a Markush claim directed to chemical compounds in an international application, there is an alternative to the "significant structural element shared by all of the alternatives" for establishing unity. This is that all the alternatives belong to a recognised class of chemical compounds in the art to which the invention pertains, but of course it is still necessary for all the alternatives to have a common activity or property.

When determining whether a group of chemical substances belong to a recognized class, the class must be one in which there is a reasonable expectation that the members will behave in the same way, in the context of the invention. However, the nature of the class should be consistent with scientific logic, and not merely a restatement of the common property. For instance, a group of enzymes that were isolated from a single organism would not be properly regarded as a class based on the organism of origin. However, if all of the enzymes also had a common or related activity, that could be the basis of a class.

The Markush concept can also be applied to a claim involving mixtures of chemicals where the components of these mixtures are selected from particular groups.  In example 33 the mixtures of herbicidal agents A and B failed this "recognised class of chemical compounds" test because the "B" group herbicides represented a plurality of classes of compounds.

Amended Reasons

Amended Reason Date Amended

Published for testing

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