Plasma levels of testosterone, androstenedione, dehydroepiandrosterone and its sulphate, and of androstenediol, as well as estrone and estradiol, were determined in several groups of postmenopausal women. The ovaries contribute to plasma estrogen levels only early in the postmenopause, but continue to secrete testosterone and minimal amounts of androstenedione throughout the postmenopause. With age there is a decreased secretion by the adrenal of dehydroepiandrosterone (sulphate) and of androstenediol. The levels of androstenedione and estrone and the androstenedione/estrone ratio remain unchanged with increasing age. The levels of estrone and estradiol, and the ratios, estrone/androstenedione and estradiol/testosterone, are correlated with fat mass. There is also an inverse curvilinear relationship with precursor concentration. This suggests either a progressive saturation of the tissular aromatase with increasing percursor level, or the existence of an unknown estrogen precursor.