Postmenopausal patients, those less than 68 years of age resistant to chemotherapy and those greater than 68 years of age with or without resistance to chemotherapy, entered this trial. Among 101 eligible patients, 46 were randomized to treatment with tamoxifen at a dose of 10 mg 3 times daily and 55 were randomized to treatment with tamoxifen at a dose of 10 mg 3 times daily plus medroxyprogesterone acetate at a dose of 100 mg once daily. Remission (partial plus complete) was obtained in 20 patients (45%) with tamoxifen compared to 14 patients (26%) with tamoxifen plus medroxyprogesterone acetate; however, this difference is not significantly different. The median duration of remission was also not significantly different between the two treatments: 10 months for the single drug compared with 9 months for the combined treatment. Response rates correlated with the presence of estrogen receptor, with no differences between the two treatment groups. Side effects occurred in 12 patients and in only one patient did they cause discontinuation of treatment. In conclusion, these results and theoretic considerations indicate that combined treatment with tamoxifen and medroxyprogesterone acetate is not better than treatment with tamoxifen alone.