PIP: The therapeutic use of estrogens for more than 25 years made it possible to examine evidence of their safety and effectiveness in a study of 292 postmenopausal women who had undergone prolonged estrogen therapy. Diethylstilbestrol and conjugated equine estrogens have been used most frequently since 1945. The study showed that only 5% of patients necessitated discontinuation from severe side effects; the latter of the 2 compounds was tolerated without side effects among almost all patients. Hot flashes were completely relieved in 93 of 94 patients. Prolonged estrogen therapy was the treatment for postmenopausal osteoporosis in 119 patients, 103 of whom had suffered collapse of vertabrae. Either complete or significant relief from pain occurred in 90%. A group of 27 women showed evidence that estrogen is a prophylactic against postmenopausal osterporosis. Justification for the fear that mammary and cervical carcinoma may result from this therapy is absent. When combined with periodic pelvic and vaginal cytological examinations, prolonged cyclic oral estrogen therapy is safe and effective treatment for postmenopausal women with disabling symptoms or osteoporosis.