Aneuploid genetic studies of isozyme variation in cv Chinese Spring have disclosed that numerous enzymes of hexaploid wheat exist in multiple molecular forms as a direct consequence of polyploidy. Sixty-nine isozyme structural genes have been identified to date. Two of these belong to a duplicate set and at least 54 to triplicate sets of paralogous genes that are located one each in related chromosomes in different genomes. Each of these gene sets encodes either two or three isozymes. The role of regional gene duplication in the production of multilocus isozymes in hexaploid wheat is as yet poorly understood, although a considerable amount of indirect evidence suggests that a large number of isozymes are encoded by genes that were produced by ancient regional gene duplication events in a genome ancestral to the genomes now present in the species. A full assessment of the role of regional gene duplication in the production of hexaploid wheat isozymes must await further studies. The isozyme structural gene locations thus far determined indicate that the gene synteny relationships that existed in the ancestral wheat genome are in large part conserved in each of the three genomes of cv Chinese Spring and that the genetic content of most individual chromosome arms has also been in large part conserved.