Elevated plasma testosterone levels were found in 8 women with Cushing's disease and oligo-or amenorrhea and/or hirsutism. In 4 men with Cushing's syndrome either due to adrenal hyperplasia or adenoma, plasma testosterone levels were lowered. Three of these 4 men complained of impotence or loss of libodo. Evidence for a major adrenal origin of the elevated testosterone values in the women with Cushing's disease was derived from the parallel suppression of cortisol and testosterone during dexamethasone administration, the testosterone responsiveness to ACTH and its dramatic fall after adrenalectomy. In the men with Cushing's syndrome the lowered plasma testosterone values were further suppressed by high doses of dexamethasone irrespective of concomitant cortisol suppression. Adrenalectomy or adenotomy restored the decreased plasma testosterone levels to normal. In women with Cushing's syndrome adrenal hyperandrogenism may account for the sexual and gonadal disturbances, in men glucocorticoid induced suppression of Leydig cell function may be responsible.