The genetics of shikimate dehydrogenase (SKDH; EC 1.1.1.25) was investigated in Triticum aestivum cv Chinese Spring (2n = 6x = 42; genomic formula ABD) using the zymogram technique. The enzyme occurs in two electrophoretically distinct forms on starch gels. The results of a study of aneuploid derivatives of Chinese Spring indicate that the SKDH isozyme of faster electrophoretic mobility is encoded by a gene, designated Skdh-A1, located in the p (= short) arm of chromosome 5A and that the products of two other genes, designated Skdh-B1 and Skdh-D1, located one each in the p arms of homoeologous chromosomes 5B and 5D, respectively, encode two isozymes of slower and coincident electrophoretic mobility. Additional evidence for this interpretation of the genetic basis of hexaploid wheat SKDH was obtained in studies of the SKDH zymogram phenotypes of various close relatives of hexaploid wheat, including T. monococcum, T. longissimum, T. tauschii, T. turgidum, and T. timopheevii.