Morning serum steroid levels were determined in postmenopausal chronic smokers and nonsmokers. Postmenopausal smokers (n = 9) had significantly elevated levels of cortisol, progesterone (P), 17-hydroxyprogesterone (17-OHP), androstenedione, and testosterone compared with nonsmokers (n = 16). The increases were most significant for cortisol (P less than 0.001) and 17-OHP (P less than 0.0005). Estrone, estradiol, dihydrotestosterone, and dehydroepiandrosterone sulfate did not differ between the groups. P to estrogen ratios tended to be higher in the smoking population. The significantly elevated P levels observed in the group of postmenopausal smokers may explain, in part, the epidemiologic finding that women smokers have a decreased incidence of endometrial carcinoma. In addition, the hypercortisolism associated with smoking may increase the risk of osteoporosis.