A multi-institutional late phase II study of KW-2307 (vinorelbine), a new vinca alkaloid derivative, in advanced or recurrent breast cancer was conducted in 26 nationwide hospitals. KW-2307 was intravenously administered at a dose of 20 mg/m2 once weekly. Eighty among the enrolled 82 patients were eligible. The overall response rate was 30.0% (24/80) with 4 CR, 20 PR, 5 MR, 22 NC, 17 PD and 12 unevaluable patients. The major side effect was leucopenia, which was the dose-limiting factor in this study. Other subjective or objective side effects included general fatigue, nausea-vomiting, anorexia, paresthesia, fever and stomatitis, but none of them was serious.