A phase-I clinical study with coadministration of a new vinca alkaloid derivative KW-2307 with cisplatin (CDDP) at 80 mg/m2 to patients with non-small cell lung cancer was conducted by a collaborative study among 6 institutions. CDDP was given on day 1 and KW-2307 on days 1, 8 and 15, both intravenously. One 28-day course was specified to be repeated twice. The initial dose of KW-2307 was 15 mg/m2 and increased to 20 mg/m2 and then to 25 mg/m2. The numbers of enrolled subjects for each dose were 5, 8 and 12 cases, respectively, in the total 25 cases. This regimen as well as KW-2307 monotherapy induced leukocytopenia (neutropenia) as the main adverse reaction. The coadministration with CDDP tended to increase the occurrence of anorexia and nausea/vomiting. Tumor response was obtained in 5 among 24 evaluable cases (CR1, PR 4). The response rate in the cases untreated with KW-2307 and given at 20 mg/m2 or higher doses was 29.4% (5/17, 95% confidence interval of the response rate: 10.3 to 54.7%). Considering drug compliance, etc., the maximum tolerated dose in this regimen was supposed to be 25 mg/m2, and the recommended dose in phase-II study to be 20 mg/m2.