From February 1983 to January 1985, 497 patients with advanced breast cancer were randomly allocated to receive either epirubicin or doxorubicin in the following combination chemotherapy regimen: fluorouracil (5-FU) 500 mg/m2 intravenous (IV) on days 1 and 8; epirubicin or doxorubicin 50 mg/m2 IV on day 1; cyclophosphamide 500 mg/m2 IV on day 1 (FEC or FAC). Cycles were repeated every 21 days until progression or to cumulative doses of 700 mg/m2 for epirubicin and 550 mg/m2 for doxorubicin. Dose reductions were applied according to the standard criteria. Activity was evaluated in 443 patients (222 in the FEC arm and 221 in the FAC arm). The two experimental groups were comparable in age, performance status, menopausal status, histology, previous treatments, and site of the disease. The overall response rate (complete response and partial response [CR + PR]) was not significantly different: 53.6% for FEC and 56.5% for FAC. The median time to progression was 273 days for FEC and 314 days for FAC; the median survival time was 591 and 613 days, respectively. Leukopenia, anemia, nausea, and vomiting were significantly lower in patients treated with FEC. As for cardiotoxicity, four cases of congestive heart failure (CHF) were recorded among patients treated with FAC while only one was observed in the FEC group. These results indicate that epirubicin in a combination chemotherapy regimen is as active as doxorubicin and is significantly less toxic.