DESCRIPTION(provided by applicant):Although there is little information available regarding age-dependent altered tissue responses to natural hormones, several lines of evidence strongly suggest that the biologic response of the vascular wall to hormones may differ in younger and older postmenopausal women. The Women's Health Initiative showed that women randomized to hormone therapy within 10 years of menopause had a relative risk less than 1 for coronary heart disease (CHD) compared with women more than 10 years postmenopausal who had a relative risk for CHD greater than 1. Nurse's Health Study data indicate that women who initiated hormone therapy within 6 years of menopause had a significantly lower CHD risk than did women who initiated therapy 6 or more years after menopause. Estrogen in the Prevention of Atherosclerosis Trial results show that estrogen therapy more effectively reduced the progression of subclinical atherosclerosis in women who were randomized within 6 years of menopause relative to those women who were 10 years or more postmenopausal. Non-human primate studies provide pathobiological evidence that the optimal time for intervention with estrogen therapy is within 6 years of menopause. With the rapidly growing number of women entering menopause and introduction of new hormonal products into the marketplace, postmenopausal hormone therapy is likely to increase. Understanding the effects of estrogen on the progression of subclinical atherosclerosis continues to be an important and timely public health issue since young postmenopausal women who have climacteric symptoms, predominantly flushing, are the women who are most likely to initiate hormone therapy. Since there are no trials designed to directly test the hypothesis that the effect of exogenous estrogen on the progression of atherosclerosis will vary by time since menopause, we propose a double-blind, placebo-controlled trial with a 2x2 factorial design (treatment x time since menopause) in which 504 healthy postmenopausal women without clinical evidence of cardiovascular disease will be randomized to 1713-estradiol 1 mg/day versus placebo according to their number of years since menopause, <6 years or >10 years. Treatment duration will average 3 years (,range, 2 to 5 years) and the rate of change _ carotid artery intima-media thickness, a well-established measure of subclinical atherosclerosis, will be the primary trial end point.