We report the fasting and post-challenge plasma insulin and glucose levels in 469 nondiabetic postmenopausal women from the Rancho Bernardo cohort according to the current use of estrogen replacement therapy. In these older women, the use of noncontraceptive estrogen was not associated with impaired glucose tolerance. Estrogen-treated women had lower levels of insulin than women who were not taking estrogen; these differences were not explained by age, obesity, or differential hormone use by women with known glucose intolerance. There were no significant differences in glucose and insulin levels in those taking conjugated equine estrogen (Premarin) alone compared to those taking it with medroxyprogesterone acetate (Provera).