5-Fluorouracil (5-FU) given by continuous infusion (c.i.) allows higher dose delivery, causes less myelosuppression, and may interfere with repair of DNA damage caused by epirubicin and cyclophosphamide. With this rationale, we conducted a phase II study to test the activity and toxicity of 5-FU c.i., epirubicin, and cyclophosphamide in patients with metastatic breast cancer (MBC). Twenty-eight patients with MBC were entered in the trial. 5-FU (200 mg/m(2)) was administered by c.i. from day 1 to day 20. Epirubicin (35 mg/m(2)) and cyclophosphamide (400 mg/m(2)) were administered from day 2 to day 4, every 4 weeks. All patients were evaluable for response and toxicity. A total of 125 courses of chemotherapy were administered, with a median of 4 per patient (range: 2--6). Toxicity, assessed using World Health Organization criteria, was as follows: nausea and vomiting grade III--IV occurred in 36%, alopecia (grade III) in 86%, neutropenia (grade III--IV) in 50%, and cardiac toxicity grade I--II in 11% of patients. Five patients (17.9%) had a complete response to therapy, and 16 (57.1%) had a partial response (response rate 75%, 95% CI 55--89%). Disease stability and progression occurred in 4 (14.3%) and 3 (10.7%) patients, respectively. Median time to progression was 13.1 months (range: 3.4--66.9+), and median survival time was 27.7 months (range: 5.4--67.1+). Outpatient treatment with combined 5-FU c.i., epirubicin, and cyclophosphamide shows high activity in advanced breast cancer and gives prolonged remission with acceptable toxicity.