This phase I study investigated the maximum tolerated dose of cisplatin, etoposide, and paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) in 18 patients with advanced small cell lung cancer. Cisplatin (80 mg/m2) and etoposide (50 or 80 mg/m2 intravenously and 100 or 160 mg/m2 orally) were infused concomitantly 30 minutes after a 3-hour infusion of paclitaxel (135, 175, or 200 mg/m2). This order of administration was known to cause less toxicity than the reverse order. Granulocyte colony-stimulating factor was given as necessary. Overall, complete responses were observed in 33% of evaluable patients and partial responses were seen in 67%. No patient progressed during therapy. Median survival exceeded 12 months, with 53% of patients alive at 1 year. Untreated patients in similar health survive approximately 6 to 16 weeks. Hematologic toxicities were seen most frequently, and neutropenia was seen most often and was the most severe. Febrile neutropenia occurred in one patient; grade 4 thrombocytopenia did not occur at all. Nonhematologic toxicity was mild. Nausea and vomiting generally were well controlled, and there were no instances of severe allergic reaction. Although the maximum tolerated dose has not yet been defined, one of two patients in the group receiving the highest doses encountered a dose-limiting toxicity. Thus, we expect to recommend the following dosages for further study: cisplatin 80 mg/m2, etoposide 80 mg/m2, and paclitaxel 175 mg/m2. All patients had an objective response and one third had a complete response, compared with 10% of patients in most series. We conclude that paclitaxel can be added safely to full doses of cisplatin and etoposide with encouraging efficacy, and recommend a randomized trial be undertaken to compare the two-drug regimen with the three-drug regimen.