This phase I study was designed to determine the maximum tolerated dose of carboplatin when administered in combination with a fixed dose of vinorelbine and concomitant radiation therapy in patients with advanced non-small cell lung cancer. Chemotherapy was administered on days 1 and 8 of two 21 day cycles. It consisted of vinorelbine at 15 mg/m(2) and carboplatin administered at an initial area under the curve (AUC) of 1.5, and increased by an AUC of 0.5 per dose level to a maximum AUC of 3, corresponding with an AUC of 6 per cycle of chemotherapy. Radiation was administered in daily fractions of 200 cGy over 5-7 weeks. We treated 36 patients, of whom 27 had stage II or III disease, and nine had stage IV disease but required thoracic radiation for palliation. Toxicities included neutropenia (three with Grade 4) and esophagitis (seven with Grade 3 and one with Grade 4). Four patients had radiation pneumonitis 4-7 months after completing therapy, three of whom died. The recommended phase II dose of carboplatin is an AUC of 3 on 2 consecutive weeks. Of 33 patients evaluable for response within the radiation field, 17 (52%) had complete or partial response, and 13 had stable disease. Of seven patients evaluable with distant metastatic disease, three had a complete or partial response, and two had stable disease. The median survival for the entire group and for patients with stage II/III disease was 13.5 months. We conclude that the combination of carboplatin, vinorelbine, and radiotherapy is feasible at these doses. It may be a useful alternative for patients not able to tolerate cisplatin-based therapy.