Irinotecan (CPT-11), a semisynthetic derivative of camptothecin, is active in the treatment of non-small cell lung cancer (NSCLC). In this report we describe our experience with this drug when used as a single agent in patients with advanced NSCLC refractory to chemotherapy with platinum and taxanes. Nineteen NSCLC patients (thirteen males and six females; 53% adenocarcinoma and 26% squamous cell carcinoma) with a median age of 52 years (range 34-71) and a Karnofsky performance status of 60% (60-80%) were included in the study. At baseline, the patients had a median of two disease sites and had been treated with a median of two prior regimens. Irinotecan was given at a dose of 100 mg/m(2) i.v.) weekly for 4 weeks followed by 1 week of rest. A total of 123 weekly infusions were administered, and each patient received a median of 4 weeks of treatment (range 1-32). All patients were evaluated by intention-to-treat analysis for efficacy and safety. Main toxicities reported were grade 3 neutropenia (10% of patients), diarrhea (10% of patients), and grade 4 thrombocytopenia (5% of patients). The overall clinical response rate was 16% (95% CI: 8-24) with three partial responses and 9 (47%) patients with stable disease. The median time to progression and the median survival time were 7 and 15 weeks, respectively. In conclusion, weekly irinotecan showed antitumoral activity and minimum toxicity in NSCLC patients refractory to platinum and taxanes.