A phase II study to test the toxicity and the efficacy of a weekly combination of Mitoxantrone, 5-Fluorouracil and L-Leucovorin (MFL) was carried out in 43 patients with metastatic breast cancer. Chemotherapy consisted of mitoxantrone 4 mg/m2, 5-fluorouracil 375 mg/m2, and L-leucovorin 100 mg/m2 on day 1, weekly. Patient characteristics were: median age 53 years (range 36-65); estrogen receptor (ER) status was known in 26 patients and of these 15 (57.7%) patients were ER-positive and 11 (42.3%) ER-negative. Of the 43 patients, 25 (58.1%) and 18 (41.9%) patients had received prior adjuvant chemotherapy and prior adjuvant endocrine treatment, respectively. MFL was administered to 22 (51.1%) patients as first line chemotherapy for advanced disease, while 21 (48.9%) patients had received 1 to 2 cytotoxic regimens for metastatic disease. The dominant sites of metastases were: soft tissue in 11 (25.5%) patients, bone in 8 (18.6%) patients and viscera in 24 (55.9%). All patients were assessable for toxicity: only 8 patients experienced WHO grade 3 leukopenia. Thrombocytopenia, diarrhea, stomatitis, and nausea/vomiting were negligible. Anemia and alopecia were not observed. Thirty-nine patients were assessable for response: overall response rate was 28.2% (complete response 7.7% and partial response 20.5%). Median duration of response was 12 months (range 6-34). Patients with no prior anthracyclines had a 42.1% response rate compared to 15% in patients who had received anthracyclines. Median overall survival of the 43 patients was 6 months (range 1-34). Weekly MFL is a well-tolerated and a moderately effective regimen for the treatment of metastatic breast cancer.