A generalized formula or description for a related set of chemical compounds, used in patent applications. It is named after Eugene Markush (1888–1968), an American manufacturer of dyes and pharmaceuticals. In 1924 he was awarded a patent for ‘The process for manufacture of dyes which comprises coupling with a halogen-substituted pyralazone, a diazotized unsulphonated material selected from the group consisting of aniline, homologues of aniline, and halogen substitution products of aniline’. Note that the patent was for processes to produce a range of compounds, including ones that had not actually been synthesized. In 1925 The US Patent Office ruled that such patents were valid. Markush structures can be described for compounds with substituents at several positions, and often many thousands of possible compounds are defined in this way. An important part of chemical database searching is the ability to find possible Markush structures to rule out priority in the patent application. Chemical drawing programs can represent such structures. For example, a bond to the centre of a ring indicates substitution at any position on the ring.