This phase I study was designed to determine the maximal tolerated doses of carboplatin and paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ), as well as the safety and efficacy of these agents, in patients with advanced, nonresectable stages IIIB and IV non-small cell lung cancer. Paclitaxel was given as a 3-hour intravenous infusion followed by a 30-minute infusion of carboplatin. Patients were assigned to one of seven treatment groups in which paclitaxel and carboplatin were given in doses ranging from 135 to 225 mg/m2 and from 250 to 400 mg/m2, respectively. Overall, the two-drug combination has been well tolerated. The major dose-limiting toxicity has not been reached but will likely be neutropenia. There appears to be a dose-response relationship: two partial responses (12%) were observed among 17 patients assigned to the lower-dose groups, whereas six (50%) of 12 evaluable patients in the higher-dose groups achieved partial responses. The maximal tolerated doses have not been reached yet, and will be at least 200 mg/m2 for paclitaxel and 400 mg/m2 for carboplatin.