Eighteen hirsute women (8 with polycystic ovarian syndrome, 10 with idiopathic hirsutism) were treated for up to 12 months with cyproterone acetate, 150 mg daily, and ethinyl oestradiol, 50 micrograms on days 5-25 of the menstrual cycle. Hair growth rate and density were measured from standardized serial photographs of a shaved skin area. A significant reduction was seen in mean hair growth rate, total plasma testosterone, free testosterone index, plasma dehydroepiandrosterone, and plasma androstenedione. LH and FSH also fell and sex hormone binding globulin level increased. No significant changes occurred in hair density or in serum PRL levels. A significant correlation was observed between hair growth rate and total plasma testosterone for the pooled results (r = 0.35, P less than 0.005). No significant correlations were seen between hair density and the endocrine parameters studied.