The efficacy of vinorelbine given as a continuous infusion was evaluated in 47 patients with breast cancer who had received previous treatment with first-line, second-line, and third-line chemotherapy including taxanes and/or anthracyclines. For inclusion into the study, patients were required to have histology-proven bi-dimensionally measurable disease. The treatment schedule was a bolus injection of vinorelbine 8 mg/m(2) administered over 5-10 minutes on day 1 followed by vinorelbine 8 mg/m(2) continuous infusion on days 1-4, every 21 days for 6 cycles. On an intent-to-treat basis, a 2% complete response rate and a 17% partial response rate were observed. The median time to progression was 2.4 months (95% CI, 1.83-2.97). Median survival was 7.73 months (95% CI, 4.48-10.98; range, 0.33-55.0 months). Major toxicities included febrile neutropenia in 40 cycles (24%) affecting 24 patients (51%) and 1 toxic death. Other nonhematologic toxicities included stomatitis (13%) and asthenia (13%). We conclude that this treatment shows considerable therapeutic activity, albeit at considerable toxicity costs, even in patients who have had multiple lines of prior chemotherapy. However, the results do not indicate clear advantages compared to the conventional weekly scheme of administration.