In an attempt to localize the source of excessive andogens in hirsute women, various steroids were determined in peripheral blood, left ovarian venous blood, and left adrenal venous blood, using radioimmunoassay techniques developed in our laboratory. Peripheral serum levels of dehydroepiandrosterone, androstenedione, 5alpha-dihydrotestosterone, testosterone, progesterone, and 17 alpha-hydroxyprogesterone were elevated in several hirsute patients, compared with those of a group of normal, cycling women of the same age. There was direct evidence to show that the ovaries and/or adrenals were secreting androgens in these hirsute patients. Saline infusion brought about minor changes in peripheral and left ovarian vein steroid levels; however, episodic fluctuations occurred in the adrenal vein samples. Adrenocorticotrophic hormone infusion brought about dramatic increases in adrenal vein steroid concentrations, while ovarian vein concentrations were unaffected, compared with peripheral steroid levels. Human chorionic gonadotropin (HCG) infusion brought about increases in left ovarian vein steroids in some patients; however, those patients with corpus luteum on the right ovary or under chronic ovarian suppression did not respond to HCG. HCG was ineffective in altering adrenal steroid secretion. It was concluded that selective venous cannulation may be of some use when the ovary is the site of excessive androgen secretion. However, care must be taken in interpreting results when a corpus luteum is present in the contralateral ovary. Interpretation is difficult when the adrenal is suspect, because of the pulsatile nature of adrenal secretion or the possibility of stress-induced secretion.