To determine whether smoking affects androgen and estrogen production and metabolism we measured the MCRs, production rates (PB), androgen and estrogen interconversions, and percent peripheral aromatization in 88 pre- and postmenopausal women grouped as smokers or nonsmokers. These women were participating in an on-going study to determine the relationship between androgen and estrogen dynamics and osteoporosis. The dynamic measurements were done using constant infusions of [3H] androgen and [14C]estrogen, and the plasma steroid concentrations were measured by RIA. We found that women who were smokers had lower MCRs for androstenedione (A), testosterone, estrone, and estradiol than those who were nonsmokers, but when the data were adjusted for body weight, the MCRs were not significantly different for any of the steroids between smokers and nonsmokers. The mean plasma A concentration was higher in the smokers than in the nonsmokers but plasma testosterone, estrone, and estradiol concentrations were not different. The PB values for all steroids, the interconversions of the androgens and the estrogens, and the peripheral aromatization of the androgens were not different in the 2 groups. These results indicate that smoking does not alter the production and metabolism of androgens and estrogens in pre- and postmenopausal women. However, because the women who smoked were less heavy than those who were nonsmokers, their androgen and estrogen MCRs were lower, leading to a greater plasma A concentration. Our data do not rule out an effect of smoking on other specific pathways of estrogen metabolism.