Thirty-five patients with metastatic breast cancer (MBC) entered a phase II study of pegylated liposomal doxorubicin 35 mg/m2 intravenously (i.v.) on day 1 plus vinorelbine 30 mg/m2 i.v. on day 1 every 4 weeks. Patients were required to have measurable disease, previous chemotherapy with an anthracycline-containing regimen, and a normal left ventricular ejection fraction (LVEF). Thirty-four patients were assessable for response and toxicity. The overall response rate (on an intent-to-treat basis) was 35% (12 of 34; 95% CI, 20%-54%). One complete response and 11 partial responses were noted. In addition, 14 patients (41%) had stable disease of > 4 months duration, and 7 patients (20.5%) had disease progression. The response rates to the combination when it was used as first- and second-line chemotherapy were 31% (4 of 13) and 38% (8 of 21), respectively. Median time to disease progression was 7 months (range, 1-35 months) and median overall survival was 13 months (range, 2 to > 62 months). Neutropenia was the most frequent toxicity (grade 4 in 44% of patients and 19% of cycles), but neutropenic fever was seen in only 3 cases. No septic deaths occurred. Nonhematologic grade 3 side effects included skin toxicity (palmar-plantar erythrodysesthesia syndrome, 6%) and mucositis (15%). Late alopecia was seen in 53% of patients (grade 1 in 41%, and grade 2 in 12%). The median LVEFs were 64% (range, 50%-81%) at baseline and 62% (range, 37%-70%) after treatment. Three patients presented an LVEF decrease to < 50%; however, no clinical heart failure was noted, and 2 of these patients recovered normal values after cessation of therapy. The combination of pegylated liposomal doxorubicin and vinorelbine can be safely administered to patients with anthracycline-pretreated MBC and is active in this population.