We performed a dose-escalation study to evaluate the maximum tolerated dose (MTD) of paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) plus a fixed dose of epirubicin. Epirubicin was administered as a 90 mg/m2 bolus immediately followed by a 3-hour infusion of paclitaxel starting at 135 mg/m2 and escalating by 20mg/m2 for each triplet of patients as long as no dose-limiting toxicity had occurred; courses were repeated every 3 weeks. The MTD was defined as that at which any of the following toxicities occurred in at least two of six patients: absolute neutrophil count less than 500/microliter for more that 7 days or less than 100/microliter for more than 3 days; any episode of febrile neutropenia requiring intravenous antibiotics and hospitalization; grade 4 thrombocytopenia requiring platelet transfusion; failure to recover absolute neutrophil count to > or = 1,500/microliter and/or platelets to > or = 100,000/microliter by day 28; and any grade > or = 3 nonhematologic toxicity. Two MTDs were defined: the first without granulocyte colony-stimulating factor (MTD 1) and the second with granulocyte colony-stimulating factor given either to accelerate recovery of grade 4 neutropenia lasting more than 72 hours or immediately in case of febrile neutropenia (MTD 2); granulocyte colony-stimulating factor was never used prophylactically. To date, 22 patients have been entered into the study; the median patient age was 55 years (age range, 30 to 66 years). Nineteen (86%) patients had received adjuvant chemotherapy that included anthracyclines in 12 cases (55%). The viscera were the dominant sites of disease in 55% of patients. Median baseline ventricular ejection fraction was 58% (range, 53% to 67%). Short-lasting grade 4 neutropenia occurred in 61% of courses; however, only four episodes of febrile neutropenia were recorded. Grade 4 thrombocytopenia was reported in 8% and grade 3 anemia in 3% of courses; four patients experienced peripheral neuropathy (three patients grade 1, one patient grade 2); complete alopecia was universal. The cardiac effects of the combination were surprisingly low: median ejection fraction at study entry was 58%, and after a cumulative dose 1,080 mg/m2 it was 56%. Three complete responses and 12 partial responses have been documented for an overall response rate of 83.3% (95% confidence interval, 58% to 96%). In conclusion, neutropenia is the most frequent toxicity of this novel combination. However, the MTD has not yet been reached. The combination of epirubicin plus paclitaxel is highly active, and no signs of cumulative myocardiopathy have been observed.