We have demonstrated the possibility of administering MAP (.) at much higher doses than was ever previously employed. Daily dosage of 1500 mg . of MAP for 30 consecutive days was an effective ( 44% CR + PR) and well tolerated treatment for advanced breast cancer. The aim of the present prospective and randomized study was to compare the above regimen with a daily dose of 500 mg . for 30 days in postmenopausal women with metastatic breast cancer. A hundred patients were admitted to the study and 46 in each group were evaluable; the groups were similar for age, duration of the disease, time from menopause, performance status, dominant metastatic lesion and previous therapy, 21 46 ( % ) patients in the 1500 group and 20 46 ( % ) patients in the 500 group showed major objective responses (CR + PR). The incidence of minimal response, no change and progression was 13, and % respectively in the 1500 mg group and , and % in the 500 mg group. When all kinds of responses as well as the incidence of progression are taken into consideration the activity of the 1500 mg regimen was significantly superior. Bone metastasis gave the best response in both groups ( 65 and 56% respectively). Mean remission duration for CR + PR was 6 + months in both groups.