A phase I trial of the combination of irinotecan (CPT-11) with cisplatin in advanced non-small cell lung cancer (NSCLC) showed a very promising response rate of 54% in previously untreated NSCLC patients. This study was conducted to confirm the activity and toxicities of CPT-11 and cisplatin combination for previously untreated NSCLC in a multi-institutional phase II study. Seventy patients with stage IIIB or IV NSCLC received CPT-11 60 mg m(-2) intravenously (i.v.) on days 1, 8 and 15, and cisplatin 80 mg m(-2) (i.v.) on day 1 every 4 weeks. Assessments were made of response, survival and toxicities. Sixty-nine were eligible, and evaluable for toxicities and survival, and 64 patients evaluable for response. Thirty-three patients (52%; 95% confidence interval 39-64%) achieved an objective response, with one complete response (2%) and 32 partial responses (50%). The median duration of response was 19 weeks and the overall median survival time was 44 weeks. The 1-year survival rate was 33%. The major toxic effects were leucopenia and diarrhoea. Grade 3 or 4 leucopenia, neutropenia, and diarrhoea occurred in 32 patients (46%), 53 patients (80%), and 13 patients (19%) respectively. A combination of CPT-11 and cisplatin is very effective against non-small-cell lung cancer with acceptable toxicities.