From October 1979 to December 1982, 126 patients with locally advanced unresectable or inoperable Stage II (7 patients), Stage IIIA (81 patients), and Stage IIIB (38 patients) non-small cell carcinoma of the lung were treated in a prospective randomized trial using five cycles of CAP (Cytoxan, Adriamycin, and cisplatin), T-CAP (triazinate plus CAP), or V-CAP (VP-16 plus CAP) chemotherapy with thoracic radiation therapy (TRT). TRT consisted of 40 Gy in 10 fractions (split-course) with cycles 3 and 4 of chemotherapy. The treatment field included the primary tumor, ipsilateral hilum, mediastinum, and ipsilateral supraclavicular fossa. All patients were followed until death or for a minimum of 5 years for survivors. The evaluable subgroup consisted of 102 patients who completed TRT. Median and 5-year survivals for the entire group were 14.0 months and 10%, respectively; for the evaluable subgroup, they were 14.8 months and 12%, respectively. There was a trend toward better survival with V-CAP plus TRT than with CAP plus TRT (p = 0.08). Median and 5-year survivals were 16.2 months and 18%, respectively, with V-CAP plus TRT. Of eight prognostic variables analyzed for their association with survival, only Eastern Cooperative Oncology Group performance status (0,1 versus 2) (p = 0.02) and weight loss (less than or equal to 10% versus greater than 10%) (p = 0.05) were significant. Sex, age, T stage, N stage, overall stage, and histologic type were not significantly associated with survival. Failure analysis revealed 83 patients (81%) with identifiable first failures. The median time to first failure was 9.8 months, and the median survival after first failure was 4.7 months. Failure patterns included local failure alone (19%), local and distant (20%), and distant alone (43%). Nineteen percent of patients had no documented progression. Total failure patterns were local in 39% and distant in 63%. Twenty-three patients (23%) had failure in the brain; they accounted for 31% of all distant failures. In 20 of these patients (20% of all patients), this was the only site of failure. There were eight (8%) initial nodal failures in 96 untreated contralateral supraclavicular fossae. No initial failures were seen in any of 101 untreated contralateral hila. The data suggest the following: (a) Combined treatment with V-CAP and TRT yielded excellent results (median survival, 16.2 months; 5-year survival, 18%).(ABSTRACT TRUNCATED AT 400 WORDS)