Serum levels of testosterone (T), 5alpha-dihydrotestosterone (DHT), androstenedione (A), dehydroepiandrosterone (DHEA), dehydroepiandrosterone-sulfate (DHEA-S), 17-hydroxyprogesterone (17-P), and cortisol (F) were measured in 33 hirsute women. Ten were hirsute and eumenorrheic (H-E), and 23 were hirsute and oligomenorrheic or amenorrheic (H-OA). Daily morning blood samples were obtained for 6 consecutive days. Dexamethasone (Dex), 2 mg/day was administered starting after venipuncture on the second day and continuing for 5 days. Human chorionic gonadotropin (hCG) was administered intramuscularly on the afternoon of the fourth and fifth days. The mean levels of all steroids measured under basal conditions in the hirsute women as a group were significantly elevated when compared to nonhirsute premenopausal women. Dehydroepiandrosterone-sulfate was the only steroid which showed significantly different mean levels between the two groups of hirsute women, being higher in the H-OA patients. Individual hirsute patients showed an elevated serum 17-P level as the most consistent finding; it was present in 90% of the patients in both groups. Significantly more H-E patients showed Dex-suppressible DHT (90% vs 40%; P less than 0.05) and A (70% vs 25%; P less than 0.05) than did H-OA patients. Dex-suppressibility of 17-P was observed in only 20% of the H-E and 15% of H-OA patients. A positive response to hCG was observed in all patients for serum 17-P and in about half or less of the patients for the other steroids. These dynamic tests of adrenal suppression and ovarian stimulation suggest that the ovary may be the main source of 17-P overproduction in both groups of patients. Although 17-P has been previously postulated to have androgenic activity, it is not yet known whether this steroid has a causal relationship to hirsutism.