A phase I study was conducted to define the maximal tolerated dose of cisplatin, ifosfamide and CPT-11 with granulocyte colony stimulating factor support in advanced non-small cell lung cancer. CPT-11 was given on days 1, 8 and 15 in combination with a fixed dose of cisplatin (20 mg/m2 i.v. on days 1-4) and ifosfamide (1.5 g/m2 i.v. on days 1-4) every 4 weeks. G-CSF (50 micrograms/m2/day s.c.) was administered on days 5 to 18, except on the days of CPT-11 treatment. The starting dose of CPT-11 was 40 mg/m2, and the dose was escalated in increments of 10 mg/m2. Forty-five patients with stage III or IV, and 35 with no prior chemotherapy, were entered in the study. The dose limiting toxicity of the combination was thrombocytopenia. The maximal tolerated dose of CPT-11 was 70 mg/m2, and the recommended phase II dose is 60 mg/m2. There were 26 partial responses among 45 entered patients for an overall response rate of 57.8%. In 35 chemotherapy-naive patients, the objective response rate was 65.7%, the median response duration was 155 days, and 1 year survival was 62.3%.