The use of estrogen replacement therapy in postmenopausal women is under close scrutiny. The indications and side effects of replacement therapy are reviewed, and recommendations regarding its use are made. Hot flashes, atrophy of the vaginal epithelium, and prevention of osteoporosis have been established as indications for estrogen replacement therapy. Prevention of cardiovascular disease, aging changes of skin, and the occurrence of mental illness have also been suggested as indications, but beneficial effects of estrogen replacement therapy for these problems have not been clearly established. Studies have shown that side effects of estrogen replacement therapy include endometrial cancer, hypertension, gallbladder disease, and angina pectoris. Breast cancer may also be a risk factor, but a consensus of opinion has not been established. Pulmonary embolism, cerebral vascular accident, or myocardial infarction has not been associated with estrogen replacement therapy. The use of progesterone with estrogen replacement therapy has been shown to reduce the occurrence rate of endometrial carcinoma, but it does not prevent all the actions of estrogen. Oral administration of estrogen is the preferred route despite misgivings about portal absorption and liver metabolism. Further studies must examine this question. Various agents have been shown to be effective in treating some climacteric symptoms. These include progesterone for hot flashes and calcium for the prevention of osteoporosis. Other agents may also be effective but have not been tested critically.