Vinorelbine (Navelbine; Burroughs Wellcome Co, Research Triangle Park, NC; Pierre Fabre Medicament, Paris, France), a semisynthetic vinca alkaloid, and ifosfamide have each shown activity as a single agent and in various combination-chemotherapy regimens against non-small cell lung cancer. Vinorelbine usually has been given on a once-weekly schedule. We designed a phase I study adding escalating doses of vinorelbine on a novel schedule of 3 consecutive days to ifosfamide in a dose-intensive regimen with granulocyte colony-stimulating factor. The goals were to define the dose-limiting toxicity and maximum tolerated dose of vinorelbine and to document the toxicity profile and the overall response and survival rates observed. Eligibility criteria included histologically or cytologically documented stage IIIB or stage IV non-small cell lung cancer, measurable or evaluable disease, and no prior chemotherapy. Treatment consisted of escalating doses of vinorelbine (starting at 15 mg/m2) on days 1, 2, and 3 and ifosfamide at 2 g/m2 and decreased to 1.6 g/m2 on days 1, 2, and 3. Granulocyte colony-stimulating factor was administered subcutaneously at 5 micrograms/kg on days 5 through 11 in all patients. Cycles were repeated every 21 days. Forty-two patients were treated. The median age was 58 years (age range, 34 to 75 years); 41 patients had a performance status of 0 or 1. Dose-limiting neutropenia was observed in two of three patients at the initial dose level of ifosfamide 2 g/m2 and vinorelbine 15 mg/m2. Ifosfamide was therefore decreased to 1.6 g/m2, and vinorelbine was subsequently escalated, with a maximum administered dose of 35 mg/m2. The recommended phase II dose was ifosfamide 1.6 g/m2 on days 1, 2, and 3 with vinorelbine 30 mg/m2 on days 1, 2, and 3, given with granulocyte colony-stimulating factor support, on a 21-day cycle. At the recommended phase II dose myelosuppression remained the most common toxic effect, with grade 3 or 4 neutropenia of brief duration occurring in 20 patients. Final analysis has not yet been completed, but responses have been observed at several dose levels. The maximum tolerated dose of vinorelbine given on days 1, 2, and 3 is 30 mg/m2 when given with ifosfamide at 1.6 g/m2 on days 1, 2, and 3 and granulocyte colony-stimulating factor support. Myelosuppression is the dose-limiting toxic effect. Future analyses of the data will report the overall response and survival rates in these patients.