Testosterone production rates in young men were measured during administration of a synthetic androgen, 2α-methyldihydrotestosterone. At levels equivalent in androgenic potency to 8 mg of testosterone, production rates were decreased 27% in 5 days and 49% in 15 days. Higher doses induced almost complete suppression of testosterone production. The administration of human chorionic gonadotropin during the continued administration of androgens caused a prompt increase in testosterone production. It is concluded that physiologic doses of androgen can inhibit the secretion of interstitial cell-stimulating hormone.