Fifteen patients with idiopathic hirsutism, who had no attenuated adrenal hyperplasia, obesity, enlarged ovaries or amenorrhea, were studied. Excessive androgen secretion by adrenal tissue was suggested by the finding of increased levels of dehydroepiandrosterone sulfate, which decreased after dexamethasone administration but did not change after human chorionic gonadotropin (hCG) injection. Excessive androgen secretion by ovarian tissue was suggested by the finding that testosterone and androstenedione levels were elevated, correlated significantly with the levels of luteinizing hormone, decreased with administration of estrogen-progestagen and increased after hCG injection. Notably, free testosterone levels, which were significantly increased, were only partially suppressed during dexamethasone or estrogen-progestagen administration. Both the adrenals and the ovaries evidently secrete androgens excessively in patients with idiopathic hirsutism.