Two postmenopausal patients with virilization had preoperative localization of ovarian tumors by selective blood sampling from both ovarian and adrenal veins and assay of hormone levels. In the first patient, the peripheral concentrations of testosterone (T), androstenedione, and estrone were 936, 1,508 and 73 pg. per milliliter, respectively, levels which are above the ranges found in normal postmenopausal women. The catheterization study showed an increase in the left ovarian vein of all hormones except cortisol. It was predicted that a tumor was present in the left ovary. At operation a 7 by 4 mm. lipid cell tumour was found. In the peripheral blood of the second patient, the T level (4,518 pg. per milliliter) was markedly elevated and the estradiol concentration (73 pg. per milliliter) was increased. At retrograde catheterization the concentration of T in the right ovarian vein was markedly elevated at 120,400 pg. per milliliter. At operation a hilus cell tumor of the right ovary was found. These two cases represent the third and fourth consecutive androgen-secreting tumors from this institution that have been localized by selective ovarian and adrenal vein catheterization and sampling.