The purpose of this multicenter phase III trial was to assess the impact of a time-intensification of FEC (fluorouracil, epirubicin, cyclophosphamide) and MMM (mitoxantrone, methotrexate, mitomycin C) regimens, supported by lenograstim (G-CSF) on the objective response rate, time to progression and survival of patients with chemotherapy-naive metastatic breast cancer (mbc). Women with mbc were randomized to receive as first-line chemotherapy either standard-dose FEC (all doses in mg/m2): arm A (500, 75, 500 every 21 days), or time-intensified FEC-G: arm B (500, 75, 500 every 14 days), or time-intensified MMM-G: arm C (mitoxantrone 10, methotrexate 35 every 14 days and mitomycin C 10 every 28 days), both with support of lenograstim (G-CSF 150 microg/m2/day s.c. for 10 days). All study treatments were administered for six cycles. Eligible female patients were in the 31-70 year range with histologically proven mbc, and measurable or evaluable disease. An intent-to-treat analysis was performed. The overall response rate (CR + PR, intent-to-treat analysis) was significantly improved in the time-intensified FEC-G regimen (69%) in comparison with standard-dose FEC (41%), p=0.002. Time-intensified MMM-G (51%) did not lead to a significant improvement in the response rate. The percentage of complete responses was significantly higher in the FEC-G arm as compared to standard-dose FEC (17% vs. 4.7%; p=0.002). The median duration was longer in the intensified-dose arms without, however, achieving a statistically significant improvement. The median time to progression (TTP), and the median survival time did not differ between the three treatment arms. Grade 3-4 leukopenia was significantly higher (p<0.001) in the standard FEC regimen-treated patients. Thrombocytopenia was significantly higher (p<0.001) in both intensified regimens. Alopecia and mucositis were significantly more frequent in both anthracycline-containing regimens (p=0.003). Other hematological and non hematological toxicities were similar in the 3 treatment arms. The increase of dose-intensity of both FEC and MMM regimens improved activity, but not efficacy as compared to standard FEC regimen in our group of chemotherapy-naive, metastatic breast cancer patients.