Three groups of indications exist for postmenopausal estrogen use: relief of symptoms related to estrogen deficiency, osteoporosis prophylaxis and treatment, and cardioprotection. Estrogen replacement therapy enhances a woman's sense of well-being and reduces the morbidity, mortality, and health care costs associated with osteoporosis and atherosclerotic heart disease. There are a few absolute contraindications to estrogen replacement therapy. Many estrogen preparations are currently available in the United States. Establishing equivalencies among the different preparations is complicated by the many physiologic and pharmacologic effects of estrogens and the variety of treatment end points used. Most estrogens have the same biologic effect provided equivalent blood levels are achieved. Estrogen replacement therapy has proved beneficial to selected postmenopausal women.