In this study the efficacy of flutamide, an antiandrogen which does not have a steroid structure, or progestational and estrogenic activities, on hirsutism and hormone levels in polycystic ovary syndrome (PCOS) and idiopathic hirsutism (IH) was investigated. Ten patients with PCOS and nine patients with IH between 19 and 36 years of age were selected for the study. They were given a 500 mg daily dose of flutamide and were followed up for clinical and hormonal effects at the second, sixth, eighth and twelfth months of the treatment. The severity of hirsutism was assessed according to the Ferriman-Gallwey's score. There was a slight decrease to below the pre-treatment level in serum LH at the end of the eighth month (P < 0.05) and there was also a persistent decrease in progesterone (P) after the second month of the treatment (P < 0.05). No other significant change was observed in ovarian or adrenal androgens. Clinical examinations revealed that after six months of the therapy the dose of flutamide had caused a significant alleviation of hirsutism and this continued during the following months.