To evaluate the effectiveness of vinorelbine (NVB) in patients with non-small cell lung cancer (NSCLC), a late Phase II study was conducted. A total of 80 patients with Stage III or IV NSCLC who had no previous therapy were entered into the study. Seventy-nine patients were eligible for response and toxicity. NVB was administered weekly by intravenous injection at a dose of 25 mg/m2 in 20 ml of saline and was generally administered in four cycles or more, unless patients had disease progression. Of the 79 eligible patients, 23 (29.1%) showed a partial response (95% confidence interval, 19.1-40.4%). The median duration of partial responses was 14.7+ weeks. The median survival time for all patients was 40.1+ weeks. The major toxicity was leukopenia. Grade 3 and 4 leukopenia occurred in 48 patients (60.8%). Other toxicities of grade 3 or more included anemia (6.3%), local cutaneous reaction (3.8%), pneumonitis (1.3%), nausea and vomiting (1.3%), mucositis (1.3%) and constipation (1.3%). The absolute dose-intensity of NVB was 22.33 mg/m2/week. A weekly schedule of intravenous administration of 25 mg/m2/week of NVB was reasonable for maintenance of activity, and acceptable for toxicity in the chemotherapy of advanced NSCLC.