Retrograde bilateral ovarian-adrenal vein catheterization was carried out in 16 patients with plasma testosterone levels exceeding 1.4 ng/ml (4.85 nmol/l). While pelvic ultrasonography and computerized axial tomographic scan failed to locate the androgen-producing ovarian tumors, catheterization led to a diagnosis of occult ovarian tumor in 5 patients, based on the observation of an abnormally-high and unilateral ovarian-peripheral vein testosterone gradient, which was subsequently confirmed histopathologically. In one case, unilateral elevation of the adrenal-peripheral vein testosterone gradient was found, complementing the ultrasonographic finding of an adrenal mass and confirming the diagnosis of a virilizing adrenal tumor. In the other 10 patients, gradient analysis ruled out an androgen-producing tumor, leading to the identification of nontumoral hyperandrogeny, such as a severe form of the polycystic ovary syndrome in the 6 premenopausal patients and of ovarian stromal and hilus cell hyperplasia in the 4 menopausal patients. In conclusion, appropriate indication of selective catheterization may considerably reduce the need for exploratory surgery and may help in selecting the adequate surgical approach.