A total of 39 women with metastatic breast cancer entered a pilot phase II study of the vindesine-mitoxantrone-mitomycin (VMMc) combination chemotherapy. Most of them had received previous chemotherapy [including doxorubicin (27 patients)] for their primary or metastatic disease. The VMMc drugs were given at usual doses. Hematologic side effects were the most serious, leading mainly to leukopenia (five episodes of infection were successfully treated). A 33% partial response rate was obtained (95% confidence limits, 18%-48%), with a median duration (not yet reached) of greater than 510 days (range, 150-720) for the overall population. The median for pretreated patients was greater than 420 days (range, 150-720) which compares favorably with those previously reported in similar patients treated by mitomycin and vindesine or vinblastine.