Given their known activity against non-small cell lung cancer, paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) and carboplatin were combined in this phase I study of patients with metastatic disease to determine the maximum tolerated dose and the dose-limiting toxicity of the combination. The initial dose of paclitaxel was fixed at 135 mg/m2 given as a 24-hour infusion with carboplatin administered in escalating doses in cohorts using Calvert's formula-dose (mg) = target AUC x (GFR + 25), where AUC is area under the concentration-time curve and GFR is glomerular filtration rate-based on target AUCs of 5, 7, 9, or 11 mg/mL.min. Dose escalations were based on cycle 1 toxicities. Filgrastim was not administered with the first cycle until two or more patients developed grade 4 or febrile neutropenia at the preceding dose level. Dose-limiting toxicity occurred in two patients at level 2 (cycle 1), and filgrastim was administered thereafter for the next four dose levels. Grade 4 thrombocytopenia was seen at level 4; thus, the carboplatin dose was de-escalated thereafter, and the paclitaxel dose escalated. Rare nonhematologic toxicities include fatigue, diarrhea, and nausea and vomiting. Among the first 30 patients, one had a complete response and 14 had partial responses, for an overall response rate of 50%. The combination of paclitaxel and carboplatin is active in non-small cell lung cancer, and the recommended phase II dose without filgrastim support is paclitaxel 175 mg/m2 via a 24-hour infusion with the carboplatin dose targeted to achieve an AUC of 7 mg/ mL.min.