Testosterone production rates were found to be elevated in 13 consecutive hirsute women, confirming previous observations. To determine the origin of the excessive testosterone, percutaneous bilateral adrenal and ovarian vein catheterizations were performed, and effluent blood samples obtained for androgen measurement. Although physical examination and retrograde dye injections failed to reveal ovarian enlargement in any of these patients, testosterone and androstenedione concentrations were higher in ovarian effluents vs. adrenal venous samples. The relative contributions of adrenal and ovarian secretion, and precursor conversion to the total testosterone production rate, were estimated in each patient from kinetic considerations and by relating the effluent concentrations of testosterone and androstenedione to the cortisol secretion rate. From such calculations, it is apparent that, in 9 of the 13 women studied, the major source of androgen was ovarian (direct ovarian secretion of testosterone and/or androstenedione which was converted to testosterone in the peripheral circulation). In the remaining 4 women, androgens originated from both the ovaries and adrenal glands. Dexamethasone was given in an attempt to suppress androgen production in all 13 patients. In the 4 women whose androgen originated from both adrenals and ovaries, there was a significant decrease in plasma testosterone and androstenedione. However, 3/9 women whose androgens originated from the ovaries similarly suppressed after dexamethasone. These studies thus suggest the ovaries as the major site of androgen production in hirsute women and cast doubt on the use of corticoid suppression tests in evaluating the site of androgen production in hirsute women.