Detailed histochemical localization of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 17 beta-HSD was made in the goat testis using both NAD and NADP coenzymes. The substrates used for 3 beta-HSD were dehydroepiandrosterone (DHA) and pregnenolone whereas 17 beta-HSD was localized with testosterone and oestradiol. In general, the activity of the enzymes varied with the cell type, substrate and coenzyme. In seminiferous tubules, DHA and NAD were the preferred substrate and coenzyme respectively for 3 beta-HSD. In addition, in interstitial tissue, NAD was the preferred coenzyme with DHA whereas no such preference existed with pregnenolone. 17 beta-Hydroxysteroid dehydrogenase showed a similar pattern in the two main compartments of the testis, as testosterone and oestradiol were equally utilized and NAD was the preferred coenzyme in both these compartments. The activities of the enzymes increased during the process of spermiogenesis and were higher in seminiferous tubules than in interstitial tissue, especially in elongated spermatids and spermatozoa.