Thirty postmenopausal patients who had evaluable estrogen receptor-positive or unknown metastatic breast cancer were treated with cyclic sequential combined hormonal therapy consisting of 50 micrograms of ethinylestradiol orally daily for 7 days followed by 400 mg of medroxyprogesterone acetate orally daily for 21 days, followed in turn by 7 days of rest. Cyclic administration was continued until progressive disease was detected. Patients who had had one previous chemotherapy regimen were included, but 63% of patients were previously untreated. Six patients achieved complete remission and 11, a partial remission, for an overall response rate of 57%. Median remission duration was 22 months; median time to disease progression for all 30 patients was 8 months. Toxicity consisted of cyclic vaginal bleeding, hot flashes, weight gain, irritability, and fluid retention. This cyclic, sequential hormonal regimen was effective and well tolerated.