This ongoing phase I study sought to establish the maximum tolerated dose of the combination of carboplatin and paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) given without routine growth factor support to previously untreated patients with stage IIIB and IV non-small cell lung cancer. Paclitaxel was administered as a 3-hour intravenous infusion. The carboplatin infusion was administered over 30 minutes immediately afterward. Patients were assigned sequentially to one of eight treatment groups in which paclitaxel and carboplatin were administered in doses ranging from 130 to 185 mg/m2 and from 230 to 350 mg/m2, respectively. Twenty-four patients have been treated to date, and the maximum tolerated dose has been reached at paclitaxel 185 mg/m2 and carboplatin 350 mg/m2. The combination has an excellent safety profile, with only a few, short-lasting episodes of neutropenia observed and no evidence of infection. At the doses tested, thrombocytopenia has not occurred.