This phase I study assessed the safety, pharmacokinetics, and efficacy of gefitinib (IRESSA) combined with vinorelbine or vinorelbine/cisplatin in chemotherapy-naive patients with advanced non-small cell lung cancer (NSCLC). Patients received gefitinib 250 mg/day and vinorelbine (group A; n = 6) or vinorelbine/cisplatin (group B; n = 8). An additional set of group B patients (n = 9) received gefitinib 500 mg/day with vinorelbine/cisplatin. Adverse events were consistent with individual treatments of gefitinib (mild reversible rash, diarrhea) and chemotherapy (asthenia, fever, nausea, vomiting, constipation), although there was a higher than expected incidence of Common Toxicity Criteria grade 3 or 4 hematologic adverse events, specifically febrile neutropenia and neutropenia. Pharmacokinetic data suggested that neither of the chemotherapy regimens affected steady-state exposure to gefitinib and also that steady-state gefitinib did not alter exposure to vinorelbine or cisplatin. Objective, durable antitumor activity was observed: five partial responses (one in group A; four in group B) and six patients with stable disease (all in group B). The safety data demonstrated that gefitinib with vinorelbine or vinorelbine/cisplatin resulted in severe myelosuppression leading to an unacceptable rate of febrile neutropenia. This study does not support the concurrent administration of gefitinib and vinorelbine, with or without cisplatin, as a valid treatment for advanced NSCLC.