Lysosomal hydrolases (e.g., acid phosphatase, AcPase; adenosine triphosphatase, ATPase, and lipase) and the mitochondrial 'marker' enzyme succinic dehydrogenase (SDH) were evaluated histochemically in the prostate gland of sexually 'quiescent' and 'active' bats. During the former state, AcPase activity was significantly less than in sexually active animals, suggesting that prostate AcPase activity is androgen dependent. Levels of lipase activity also were highest in the prostate of sexually active bats, suggesting the importance of endogenous lipids which may be mobilized and used as a source of energy. SDH and ATPase sites and patterns of distribution in the prostate gland of bats were closely similar during the two reproductive states. Differential enzymological patterns do not seem to have any significant correlation with the morphological changes which occur in the glandular epithelium, musculature, urethra and the luminal fluid, as the animals pass from a 'quiescent' phase to one of activity and vice versa as observed in the present study.