The plasma concentrations of total testosterone, free testosterone index, androstenedione, 17 beta-estradiol, luteinizing hormone, follicle-stimulating hormone, prolactin, and urinary 17-ketosteroid and 17-ketogenic steroid excretion were measured in 48 nonhirsute and 119 hirsute patients. Hormone data were compared within and between groups according to whether the menstrual cycles were eumenorrheic, amenorrheic, or oligomenorrheic. Eleven hirsute women treated with prednisone were followed for 6 months. It was concluded that: (1) androstenedione, testosterone, free testosterone index, and adrenal androgens alone or in combination play a role in the pathogenesis of the hirsutism observed in eumenorrheic women and in the amenorrhea and oligomenorrhea of both hirsute and nonhirsute women; (2) body weight correlated with adrenal adrogens (17-ketosteroids) in nonhirsute women and with androstenedione in hirsute women; (3) prednisone significantly suppressed androstenedione and 17-ketosteroids (p less than 0.05), with a decline of testosterone to 65% and luteinizing hormone to 51% of pretreatment values, with favorable clinical effects on the hirsutism, menstrual dysfunction, and infertility; (4) concentrations of 17 beta-estradiol were lower in amenorrheic than in eumenorrheic and oligomenorrheic women of both groups.