A phase I trial of paclitaxel therapy, administered as a weekly 3-h infusion for 6 weeks with concurrent daily thoracic radiation to patients with advanced or medically inoperable non-small cell lung cancer, was performed. Paclitaxel was escalated in increments of 10 mg/m2/week in successive cohorts of three new patients as tolerated, starting at 10 mg/m2/week. Radiation was administered to the primary tumor and regional lymph nodes (40 Gy over 4 weeks), followed by a boost to the primary tumor (20 Gy in 2 weeks). Twenty-seven patients entered this study through seven dose levels of paclitaxel ranging from 10-70 mg/m2/week for the primary purpose of evaluating the toxicity of concurrent chemoradiation treatment. Esophagitis was the principal and dose-limiting toxicity. Radiation pneumonitis occurred in two patients. Other toxicities were mild. Although not designed as an efficacy study, 23 patients were available for response, and an overall response rate of 74% (confidence interval, 65-83%) was observed.