To study the contribution of adrenal glands to circulating estrogens in woman, the concentrations of estrone (E1), estradiol-17 beta (E2), and estriol (E3) in adrenal and peripheral venous blood were measured by radioimmunoassay and the grandular secretion of estrogens after ACTH stimulation was investigated by analyzing the adrenal vein levels of these steroids in patients with breast cancer who were undergoing a therapeutic adrenal operation. Furthermore, adrenal secretion rates of estrogens and cortisol were estimated. It was shown that there existed greater concentrations of estrogens in adrenal vein than in peripheral blood; about 3 times higher for E1 (p less than 0.001), and 2 times higher for E2 and E3 (p less than 0.05). Administration of ACTH caused a significant increase of E1 and E2 concentrations in adrenal venous blood to mean 150% of the basal levels that was comparable to the increase of cortisol. Apparent adrenal secretion rates of estrogens estimated under surgical situation were calculated to be 7.7 +/- 1.7 (M +/- SE) microgram/day for E1, 1.9 +/- 0.3 microgram/day for E2, and 0.3 +/- 0.2 microgram/day for E3, while the secretion rate of cortisol was 52.7 +/- 8.2 microgram/min. The present study demonstrates that the direct adrenal secretion of not only E1, but E2 and E3 contributes to the circulating estrogen levels, and it is suggested that the adrenal glands might be responsible for the relatively important source of estrogen production in the aged woman.