Thirty-one patients with previously untreated advanced non-small cell lung cancer were included in a Phase I study to determine the optimal dose of Carboplatin (CBDCA) which preserves the best Navelbine (NVB) dose-intensity. NVB was administered at a 30-mg/m2 fixed-dose on days 1-8/q 3 weeks, whereas CBDCA doses were planned to be escalated from 275 to 400 mg/m2 on day 1/q 3 weeks for six successive groups of patients. The toxicity limiting dose of CBDCA in the combination was 350 mg/m2 on day 1/q 3 weeks because of repetitive Grade IV neutropenia, and the optimal dose of CBDCA was 325 mg/m2 on day 1/q3 weeks, offering a 86.4% NVB and a 92.6% CBDCA relative dose-intensity for the first 9 weeks. Responses were observed at each step. This study demonstrates the feasibility and the efficacy of the NVB-CBDCA combination. It suggests that dose-intensity calculation can be helpful to determine the recommended dose for Phase II studies of new drug combinations.