Objective: To compare the clinical and endocrinologic effects of cyproterone acetate (CPA), an antiandrogen with progestational activity; flutamide, a nonsteroidal antiandrogen, and finasteride, an inhibitor of 5 alpha-reductase. Design: Randomized, open, controlled clinical study. Setting: Department of Obstetrics and Gynecology, University of Pisa, Pisa, Italy. Patient(s): Forty-five hirsute women were enrolled in the study: 29 were hyperandrogenic and 16 had idiopathic hirsutism. Three women dropped out of the study. Intervention(s): Women were randomly treated with finasteride (5 mg/d; n = 14), CPA (25 mg plus ethinyl E-2 (EE); n = 13), or flutamide (500 mg/d; n = 15) for 1 year. Main Outcome Measure(s): Hirsutism was assessed using the Ferriman-Gallwey method. Levels of total and free T, androstenedione (A), DHEAS, sex hormone-binding globulin, dihydrotestosterone, and 3 alpha-androstanediol glucuronide were evaluated at the beginning of the study and every 3 months. Result(s): Treatment with finasteride, flutamide, and CPA significantly decreased the Ferriman-Gallwey score. The percent decreases in the hirsutism score induced by the different treatments were similar. Treatment with CPA plus EE significantly decreased levels of total and free T, A, dihydrotestosterone, and 3 alpha-androstanediol glucuronide. These parameters were unchanged with flutamide therapy. Finasteride significantly increased total T levels but reduced dihydrotestosterone and 3 alpha-androstanediol glucuronide concentrations. Conclusion(s): Finasteride, CPA, and flutamide are equally effective in decreasing hirsutism, despite different mechanisms of action. (Fertil Steril(R) 1999;71:445-51. (C)1999 by American Society for Reproductive Medicine.).