We studied the simultaneous responses of four serum androgens (testosterone, androstenedione, dehydroepiandrosterone, and dehydroepiandrosterone sulfate) and five other steroids (deoxycorticosterone, corticosterone, 11-deoxycortisol, cortisol, and 17 alpha-hydroxyprogesterone) to the infusion of small amounts of cosyntropin in eight patients with idiopathic hirsutism and in six normal women. Serum testosterone and androstenedione concentrations were significantly higher in hirsute women after graded cosyntropin infusions than in controls, as were concentrations of plasma deoxycorticosterone and 11-deoxycortisol. Analysis of the substrate/product ratios 11-deoxycortisol/cortisol and deoxycorticosterone/corticosterone revealed defective 11 beta-hydroxylation in women with hirsutism. The presence of increased circulating androgen levels in response to physiologic amounts of adrenocorticotropic hormone thus appears to be a common response in women with idiopathic hirsutism, and, together with impaired adrenal 11 beta-hydroxylation, points to an adrenal defect as important components of this disorder.