Mature and young adult rats were treated with a single dose of 115 mg and 50 mg of pipecolinomethylhydroxyindane (PMHI) maleate per kg of body weight. Large intraperitoneal doses were toxic in mature rats and the growth of younger animals were retarded by the lower subcutaneous dose. In both instances, PMHI caused a rapid reduction in testis weight with arrested spermatogenesis. Atrophic changes to the ventral prostrate and the lowering of blood testosterone levels suggests that the actions of PMHI are not strictly confined to the seminiferous tubules. This was further substantiated by the demonstration of direct inhibition by PMHI of testicular androgenesis in vitro. The actions of PMHI on steroidogenesis may be readily reversible and, compared to tubular actions, are of a minor nature. There were no clear-cut adrenocortical responses to PMHI administration but there was some depression of adrenal gland weight, plasma corticosterone, and aldosterone.