The purpose of this study was to quantify the various sources of estrone (E1) and 17 beta-estradiol (E2) production in normal men and in women with testicular feminization. The mean production rate of E1 in four young adult men was 58 micrograms/24 h, while that of E2 was 44 micrograms/24 h. In these men, E1 production could be accounted for totally by extraglandular formation through 1) aromatization of plasma androstenedione, 2) conversion of E2 which was formed from the aromatization of plasma testosterone, and 3) conversion of secreted E2. In these men, only 12 micrograms or less of E2 production could not be accounted for by extraglandular formation from plasma C19 precursors, and is presumed to have arisen by testicular secretion. In six women with testicular feminization, the mean production rate of E1 was 99 micrograms/24 h, while that of E2 was 77 micrograms/24 h. THe amount of E2 production that arose by glandular secretion could be computed in four of these women and was considerably greater than that found in the young adult men. In these women with testicular feminization, an average of 44 micrograms/24 h E2 could not be accounted for by extraglandular formation and is presumed to have arisen by testicular secretion. The mean plasma production rate of testosterone in the normal men was 5.7 mg/24 h, while that in the women with testicular feminization was 8.3 mg/24 h. However, the range of plasma production rates of testosterone in the women with testicular feminization was large (1.3--17.0 mg/24 h).