The effects of oral administration of cyproterone acetate (CPA) (50 mg) associated with natural estrogens, was investigated in two groups of hirsute women. One group received 17-beta estradiol valerianate (E2) (2 mg) (n = 22) and the other, micronized E2 (2 mg) plus estriol (E3) (1 mg) daily (n = 22) for 21 days every month. After a six month period of treatment, hirsutism improved in 70% of the patients. The more frequent adverse effect was amenorrhea. Except in one, weight gain was prevented by a low calorie diet in overweight patients. During treatment, the plasma concentration of E2 was within the normal range for the follicular phase, whereas estrone was higher, and significantly (p less than 0.001) higher under E2 + E3 than under E2 alone (43.5 +/- 29.1 vs 23.9 +/- 6.1 ng/dl). The binding capacity of sex-steroid binding-protein (SBP) was increased by E2 + E3, and was not affected by E2; transcortin levels were unchanged during treatment. The plasma levels of SBP-unbound testosterone and of delta 4-androstenedione were significantly suppressed by CPA, while DHEAS was not significantly reduced. We concluded that oral administration of CPA and natural estrogens, is a well tolerated and efficient treatment of hirsutism.