Gonadotropins, estradiol (E2), and the steroid precursors of ovarian estrogen secretion were examined in women on danazol to clarify actions of the medication on hypothalamic-pituitary-ovarian function. Follicle-stimulating hormone was not altered acutely after a single maximal dose or chronically during therapy, whereas a slight but significant increase in luteinizing hormone was noted during the 6 months of treatment. During danazol treatment, there was a blunted response of E2 to injections of human menopausal gonadotropins. The progestin and androgen precursors of E2 were reduced, with the exception of 17-hydroxypregnenolone, which was significantly increased. This 17-hydroxylase enzyme block persisted in spite of dexamethasone suppression of adrenal function. Therefore, the reduced ovarian secretion of E2 in women receiving danazol is due in part to reductions of ovarian precursor steroids for E2 synthesis, consequent to a direct ovarian action of the medication.