In hypophysectomized immature female rats (HIFR), the ovarian weight response to subcutaneously implanted diethylstilbestrol capsules (DESC) is inhibited by small doses of human chorionic gonadotropin (hCG). This effect, reproduced by equivalent doses of interstitial cell stimulating hormone (ICSH) but not by follicle-stimulating hormone (FSH), is inhibited by treatment with antiandrogens. These data implicate gonadotropic stimulation of interstitial cell androgen production in the control of follicular maturation in rats.