Previous studies have shown a relationship between age and weight and the MCR and conversions ([rho]) of androgens and estrogens. To assess the relative importance of these relationships in the metabolism and conversion of the androgens and estrogens, we used a series of statistical analyses, including t test, Pearson's correlation, and a step-wise regression analysis of the data obtained from the constant infusion of radiolabeled androgens and estrogens to normal women, 18-90 yr old. The MCRs of testosterone (T), androstenedione (A), and estrone (E1) were strongly correlated with weight, but not age or menopausal status. The MCR of estradiol (E2) was strongly correlated with weight and less strongly correlated with age, but was not correlated with menopausal status. The interconversions of the androgens ([rho]T,ABB and [rho]A,TBB, i.e. percentage of precursor infused measured as product in blood) and estrogens ([rho]E1,E2BB and [rho]E2,E1BB) were not correlated with age or weight, but there was a weak correlation between [rho]T,ABB and menopausal status. The aromatization of androgens to estrogens ([rho] A,E1BM and [rho]T,E2BM, i.e. percentage of androgens infused measured as estrogen glucuronide in the urine) was highly correlated with age, less strongly correlated with weight, and not correlated with menopausal status. The correlation with weight and MCR is a reflection of the extrasplanchnic metabolism of steroids. The lack of correlation with weight for the interconversions of androgens and estrogens indicates that the enzyme(s) responsible is affected differently in extrasplanchnic tissue than is the aromatase complex. The relationship between age and aromatization, while strong, remains unexplained.