A glucose oxidase (GO) has been identified in the ejaculatory duct of male Drosophila melanogaster. Evidence is given that this enzyme was previously misidentified as HEX-1. Genetic analysis indicates that the Go structural gene is located on the third chromosome at 48 + or - 0.5 cm. Go is polymorphic in males in populations of D. melanogaster and D. simulans located in Athens, Georgia. Two other hexose enzymes have also been tentatively identified for the first time in Drosophila. These are NAD(P)-glucose dehydrogenase (GODH) and NAD-gluconate dehydrogenase (GNDH). GODH and GNDH are found in both males and females and may circumvent the initial steps in the pentose shunt.