In order to verify the anti-androgenic effects of canrenone, the major metabolite of spironolactone, 9 normally cycling women with post-puberal hirsutism, were orally administered the drug (200 mg per day for three months). In all patients, the clinical score, according to the method of Ferriman and Gallwey (F.G.I.: Ferriman-Gallwey Index), as well as endocrine function tests, including total and free testosterone, sex hormone binding globulin, dehydroepiandrosterone sulphate, 17-OH-progesterone, basal and ACTH stimulated cortisol, were evaluated prior to and after canrenone treatment. A significant reduction in hair growth (F.G.I. = 18 +/- 2 vs 23 +/- 3, p less than 0.001), and also a significant decrease, with regard to endocrine parameters, of total testosterone (0.5 +/- 0.1 vs 0.9 +/- 0.3 p less than 0.01), free testosterone (2.7 +/- 0.7 vs 4.7 +/- 1.7, p less than 0.005), dehydroepiandrosterone sulphate (228 +/- 38 vs 314 +/- 81, p less than 0.02), and sex hormone binding globulin (62.5% of basal values, p less than 0.001), were observed. Serum levels of 17-OH-progesterone, and basal and ACTH stimulated cortisol were not significantly different from pretreatment values. It is concluded that the biochemical and clinical parameter improvement, along with a well-preserved cortisol secretion (unchanged levels of 17-OH-progesterone), suggest that canrenone may represent an effective therapy for idiopathic post-puberal hirsutism.