The incidence of atherosclerotic cardiovascular disease in women does not approach rates seen in men until approximately a decade following menopause, suggesting that estrogen is vasculoprotective. Infectious pathogens such a Chlamydia pneumoniae (C. pneumoniae) and human cytomegalovirus (hCMV) have been implicated in the pathogenesis of atherosclerosis. Experimental studies in cultured lymphocytes and animals suggest that estrogen stimulates cell-mediated immune responsiveness, observations that are potentially relevant to the eradication of intracellular pathogens including C. pneumoniae and hCMV. The purpose of this study is to determine whether estrogen therapy augments cell-mediated immune responsiveness in estrogen-deficient postmenopausal women who have serologic evidence of chronic infection with C. pneumoniae and/or hCMV. A comparison will be made between seropositive and seronegative women. We propose that estrogen therapy will stimulate a more efficient cell-mediated response to these chronically persistent infectious intracellular pathogens, resulting in eradication of these organisms that are of potential importance in atherogenesis.