We conducted a phase II study to determine the activity and tolerability of weekly epirubicin-paclitaxel and granulocyte colony-stimulating factor in breast cancer patients untreated for metastatic disease. The phase II study was designed following the Simon optimal-two stage method. Patients received epirubicin 25 mg/m and paclitaxel 80 mg/m every week, and granulocyte colony-stimulating factor on days 2 and 4 for 24 consecutive weeks in the absence of progression. From 1999 to 2004, 53 patients entered the study; 1093 weekly courses were delivered, with a median number of cycles of 22. Patients received a median relative dose intensity of 94%. No hematological grade 3-4 toxicities were observed. One patient had one episode of grade 3 mucositis and two patients (3.8%) suffered grade 2 asthenia. Eight patients (15.1%) experienced grade 2 neutropenia, grade 2 anemia was registered in seven patients (13.2%). No cardiotoxicity was observed. Ten out of 53 patients (18.9, 95% confidence interval 8.3, 29.4%) showed a complete response, whereas 28 (52.8, 95% confidence interval 39.4, 66.3%) had a partial response, with an overall response rate of 71.7% (95% confidence interval 59.6, 83.8%). In addition, 14 patients (26.4%) had stable disease. Median time to progression was 12 months (95% confidence interval 7, 17). Median response duration was 14 months (range 3-60). The 1-, 3- and 5-year survival rates were 90.1, 68.0 and 56.6%, respectively. In untreated metastatic breast cancer patients, the weekly administration of epirubicin and paclitaxel with granulocyte colony-stimulating factor support seems to be extremely tolerable and active, and deserves further investigation into a phase III trial.