Comparisons were made of the oxidative and glycolytic activity and rate of lipid synthesis between washed cauda epididymal and ejaculated bull spermatozoa in the presence of selected androgens*. No significant difference was observed in the metabolic pattern of the two types of spermatozoa when incubated with no added androgen. With the exception of testosterone, androstenedione and 5β-androstanediol, the added androgens, at a concentration of 100 μg/ml, depressed the oxidative metabolism of epididymal and ejaculated spermatozoa. Glycolysis in epididymal and ejaculated spermatozoa was markedly stimulated in the presence of testosterone, androstendione or androstanedione, and the magnitude of this response was similar in both types of cells. Dihydrotestosterone enhanced glycolysis in ejaculated but not epididymal spermatozoa, whereas 5β-androsterone increased the glycolytic activity only in epididymal spermatozoa. Under anaerobic conditions, only androstanedione was effective in stimulating the rate of glucose dissimilation to lactic acid by epididymal spermatozoa, but exposure to seminal plasma of the epididymal spermatozoa before incubation eliminated this effect on the subsequently washed cells. Epididymal and ejaculated spermatozoa incubated with no added androgen incorporated similar amounts of [U-14C] glucose into lipid. The addition of androgens increased or tended to increase lipid biosynthesis from glucose in both types of spermatozoa. Androstanedione was the most effective androgen in altering glucose metabolism and lipid synthesis in epididymal and ejaculated spermatozoa. It is concluded, that, although there are subtle differences between epididymal and ejaculated spermatozoa in their response to certain androgens, they are essentially the same cells as judged by their pattern of glucose metabolism.