Two groups of 23 patients each, having advanced breast cancer, entered this prospective and randomized study. One group was treated with the conventional schedule of CMF (cyclophosphamide 100 mg/m2/po from the first to the 14th day, methotrexate 40 mg/m2/iv the first and the 8th day, 5-fluorouracil 600 mg/m2/iv the first and the 8th day), and the other was treated with a new six-drug regimen, administered at low doses (R 14: cyclophosphamide 2 mg/kg/iv, vincristine 0.01 mg/kg/iv, vinblastine 0.1 mg/kg/iv, the first day and 5-fluorouracil 5 mg/kg/iv, methotrexate 0.7 mg/kg/iv, adriamycin 0.5 mg/kg/iv the 2nd day every 21 days). The remission rate was 35% (8/23) and 39% (9/23) for CMF and R 14 respectively. The median duration of objective remission was 6 months for CMF and 5 months for R 14 regimen. The median survival time of responding patients was 18 months for CMF and 14 months for R 14. This study shows that the new six-drug regimen at low doses is effective (regarding subjective, objective response and survival rate), and its toxicity is no higher than that of CMF (the incidence of leukopenia was significantly lower during the first course). Therefore, R 14 should be considered an alternative regimen to CMF in the treatment of advanced and, possibly, early breast cancer. The advantages for using R 14 are: 1) it is less toxic (a single dose is a very small amount of medicine compared to what is usually administered), 2) an iv administration always follows a therapeutic program (while in a CMF schedule cyclophosphamide is self-administered by the patient).