The purpose of this study was to examine the safety and efficacy of carboplatin/etoposide/paclitaxel in patients with untreated stage IV non-small-cell lung cancer (NSCLC) and extensive small-cell lung cancer (SCLC). Carboplatin was administered intravenously (i.v.) at an area under the curve (AUC) of 6 with etoposide at either 80 or 100 mg/m2 i.v. days 1-3 and paclitaxel at 175 or 200 mg/m2 i.v. over 3 hours along with 5 g/kg of granulocyte colony-stimulating factor subcutaneously on days 4-18, repeated every 3 weeks for 6 courses. Thirty-one patients (five NSCLC and 26 SCLC) entered into this phase I study. The median age was 63 (range, 42 to 74 years), with 24 males and seven females. The recommended dose level for phase II testing was carboplatin AUC = 6, etoposide 80 mg/m2 days 1-3, and paclitaxel 175 mg/m2 over 3 hours. With seven patients at this level, 14% had grade 4 neutropenia, 14% had grade 4 thrombocytopenia, none had grade 2/3 neurotoxicity, and no toxic deaths occurred. One of five (20%) patients with NSCLC responded, and 19 of 22 (86%) evaluable SCLC patients experienced a response to therapy. SCLC patients had a median survival of 10 months. The combination of carboplatin/etoposide/paclitaxel has significant activity with acceptable toxicity in patients with extensive SCLC.