Twelve women, 11 with hirsutism and one with alopecia areata, were treated with low-dose spironolactone (50 mg daily) from the 4th until the 22nd cycle day over 12 consecutive menstrual cycles. Eight hirsute women observed a favorable effect on hirsutism in 3 to 8 months, and hair loss ceased in the one patient with alopecia areata. No significant side effects occurred. Low-dose spironolactone decreased the concentration of total and free testosterone and elevated the concentration of prolactin on the 10th cycle day, while LH, FSH, estradiol, progesterone, DHEAS, SHBG, and cortisol levels remained unchanged. The plasma aldosterone concentration increased significantly during the treatment, although serum potassium and sodium concentrations remained unchanged. Low-dose spironolactone is, thus, safe and effective in the treatment of hirsutism. It seems to be useful as an initial or alternative treatment.