A multicenter early Phase II clinical study of KW-2307, a new vinca alkaloid derivative, in patients (pts) with lung cancer was conducted in 15 hospitals. Ninety-seven pts were enrolled, among whom 95 were eligible. Seventy of the eligible pts had non-small cell cancer (NSCLC) and 25 had small cell cancer (SCLC). PR was obtained in 13 (18.6%) of NSCLC pts and 3 (12%) of SCLC pts. Only those who had no previous chemotherapy showed PR in NSCLC pts, and the response rate in these pts was 29.5% (13/44). As to the correlation between dosage and tumor effect, a better effect was exhibited at higher doses, with response rates of 21.7% (5/23) and 38.1% (8/21) at 20 mg/m2 and 25 mg/m2, respectively. The major adverse effect of this drug was leukopenia (neutropenia), which was Grade 3 or 4 in many cases. Recovery from this complication, however, was rapid. Other adverse effects included mild hepatic dysfunction, anorexia, nausea/vomiting, fever, general fatigue, phlebitis and constipation. The incidence of peripheral nervous disorder such as the paresthesia commonly observed with vinca alkaloids, was as low as 10%, and the symptoms, if any, were mild.