Irinotecan (CPT-11), a topoisomerase I inhibitor, has been shown in preclinical studies to be a potent radiosensitizer. Carboplatin, a known radiosensitizer with single-agent activity in non small-cell lung cancer (NSCLC), is felt to be a rational choice in combination with irinotecan. We have completed the initial portion of a phase I study, in patients with locally unresectable lung cancer, combining irinotecan with thoracic radiation. Thirteen patients have been entered onto this study through three dose levels (30 to 50 mg/m2/week) of irinotecan. There were seven partial responses in 12 evaluable patients, for an over-all response rate of 58%. Nausea, vomiting, and esophagitis were the principal toxicities of weekly irinotecan and concurrent thoracic radiation. As the maximum tolerated dose (MTD) of irinotecan with radiation has been established at 40 mg/m2/week, we are currently accruing patients to the second phase of this study with the addition of carboplatin (AUC = 2). Thus far toxicity has primarily been esophagitis.