A phase II study was conducted to assess the activity and toxicity of irinotecan (CPT-11) and carboplatin (CBDCA) combination chemotherapy for advanced non-small-cell lung cancer (NSCLC). Eligibility included chemo-naive advanced NSCLC patients with measurable disease and a good performance status. CPT-11 of 50 mg/m(2) was administered as a 90-min intravenous infusion on days 1, 8, and 15. CBDCA dosed to an area under the concentration-time curve of 5 mgmin/ml, using Calvert's formula, was administered by 90-min infusion after the CPT-11 infusion on day 1. Treatment was repeated 28 days interval for at least two cycles. Haematopoietic growth factors were not routinely used. From December 1997 to January 1999, 36 patients were entered into the study. The overall response rate was 25.0% (95% confidence interval: 12.1-42.2%). The median survival time and the 1-year survival rate were 10.2 months and 42.2%, respectively. Major toxicity by Japan Clinical Oncology Group criteria was as follows: grade 3-4 neutropenia 76.5%; grade 3 anemia 26.5%; grade 3/4 thrombocytopenia 47.1%; grade 3 nausea/vomiting 36.1%; grade 3-4 diarrhoea 5.9%; grade 3 alopecia 5.9%; grade 3-4 skin rush 2.9%. Four patients developed febrile neutropenia and only one had serious diarrhea induced by CPT-11. Actual relative delivery dose of CPT-11 to the projected one on days 8 and 15 were 0.86 and 0.43, respectively. It seemed that CPT-11 and CBDCA was more toxic regimen than CPT-11 and CDDP in advanced NSCLC. The relatively disappointing response rate could be related with low dose intensity of CPT-11.