The purpose of this study was to determine the feasibility of additional chemotherapy beyond 5 weeks of vinblastine-cisplatin followed by radiation therapy for patients with stage III non-small cell lung cancer. In this randomized phase II trial, the goal was to determine, in a similar population of patients, the toxicity of either of two additional chemotherapy programs. Ninety-one patients with stage III non-small cell lung cancer received the same induction regime of vinblastine/cisplatin/radiotherapy. In patients randomized to regime 1, an additional four cycles of vinblastine/cisplatin were given after the radiotherapy. In regimen 2, six weekly doses of carboplatin were given concurrent with the radiotherapy. The additional four cycles of vinblastine and cisplatin were completed by 34% of patients; the concurrent carboplatin program was completed by 70% of patients. Grade 3 or 4 granulocytopenia occurred in 53% of patients on regime 1 versus 17% on regime 2 (p < 0.003); grade 3 or 4 nausea/vomiting occurred in 20% of those on regime 1 versus 7% on regimen 2 (p = 0.175). Response rates and survival were similar for the two regimens, with approximately 30% of patients surviving at 2 years. Given the reduced toxicity and the improved capacity to complete the planned therapy with the concurrent carboplatin treatment, this regimen will be further examined in a phase III trial.