This report describes the preliminary results from a randomized study comparing megestrol acetate with tamoxifen in the treatment of postmenopausal women with advanced breast cancer, correlating estrogen receptors (ER) and progesterone receptor (PgR) status with response. Patients received megestrol acetate (40 mg) orally four times daily or tamoxifen (10 mg) orally twice daily. If the initial therapy failed, patients were crossed over to the alternate treatment. Of 197 patients entered in the study, 190 were considered evaluable. The overall response rates were 35% with megestrol acetate and 42% with tamoxifen. Twenty-three percent ( 7 30) of patients responded to megestrol acetate after being crossed over from tamoxifen, while 22% ( 6 27) responded to tamoxifen after being crossed over from megestrol acetate. Response did not correlate significantly with combined receptor (ie, ER plus PgR) levels. A significant trend was seen between ER level and response only in the tamoxifen group. There was no association between PgR levels and response for either tamoxifen or megestrol acetate. © 1986.