A randomized controlled trial was performed to compare the therapeutic results of oral high-dose medroxyprogesterone acetate (HD-MPA) versus mepitiostane (MS) in the treatment of postmenopausal breast cancer. MPA was given at three doses of 400 mg orally daily to 47 patients and produced objective responses in 19 cases (40.4%). An objective response was seen in 14 of the 40 control patients given MS at two doses of 10 mg orally daily (35.0%). Among patients with bone metastases, 6 of 19 (31.6%) for HD-MPA and 2 of 13 (15.4%) for MS showed objective responses. The other merits of HD-MPA suggested in the study were improvement in performance status, increase in appetite, and myeloprotective effect.