The glucose dehydrogenase gene (Gld) in Drosophila melanogaster exhibits a unique spatial and temporal pattern of expression. GLD expression switches from a non-sex-limited state at the pupal stage to a male-limited state at the adult stage. At the adult stage, the enzyme is restricted to the ejaculatory duct. Within the genus Drosophila, the ejaculatory duct has undergone a simple morphological divergence. In order to determine whether correlated changes in GLD expression had occurred, GLD activity during the pupal and adult stages was determined for several Drosophila species. It was found that virtually all of the species exhibit pupal GLD activity, whereas only those species with an expanded ejaculatory duct express male-limited GLD. The results of interspecific genital imaginal disc transplantation experiments indicate that the expanded morphology and GLD expression do not require any species- or sex-specific diffusible factors. An apparent regulatory polymorphism exists within the D. takahashii species with respect to male-limited GLD expression.