Danazol (200 mg/day) or placebo was administered to patients with premenstrual syndrome from the onset of symptoms until the onset of menses, for two cycles each, in a prospective, double-blind, crossover design. Eleven of 14 patients improved on danazol. The symptom scores with danazol were significantly lower than those with placebo (P less than .035). No side effects were reported from the medication. We conclude that danazol, given periodically and in a relatively low dose, appears to have a beneficial effect in the treatment of premenstrual syndrome.