Total testosterone, dehydroepiandrosterone sulfate, prolactin and estradiol were assayed in 78 women, clinically divided into idiopathic hirsutism (I. H.)-17 women and polycystic ovary syndrome (PCO) - 61 women, with the latter group having menstrual irregularity dating almost back to the menarche. The serum testosterone measurement was found to be not sensitive in detecting abnormalities in testosterone production. Only 24 (39%) of the women with polycystic ovary syndrome and 5 (29%) of the women with idiopathic hirsutism had elevated serum testosterone. In statistical analysis the serum testosterone was greater (P less than 0.05) in women with polycystic ovary syndrome without hirsutism than in idiopathic hirsutism and PCO with hirsutism. There were not significant differences between the mean levels of prolactin, dehydroepiandrosterone sulfate and estradiol. Twelve women, with hirsutism, were treated with low dose spironolactone (75 mg daily) for six months. There was an excellent clinical response in 7 (58%), incomplete response in one, no response in 4 women. Two patients dropped out of the trial because of ineffectiveness of the therapy after three months. Side effects were not major problem. Spironolactone caused statistically significant reduction in testosterone values after 6 months of treatment. Our results demonstrate that low-dose spironolactone is effective in the treatment of hirsutism.