The University of Colorado Cancer Center is conducting a phase I study of the three-drug PET combination of cisplatin, etoposide, and paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) in patients with advanced (stage IV or IIIB with pleural effusion) small cell lung cancer. The primary study goal was to define the maximally tolerated doses given on an outpatient basis. Secondary goals were to determine toxicities, response rate, response duration, and survival. Paclitaxel was given as a 3-hour intravenous (IV) infusion prior to cisplatin and etoposide. The starting doses were paclitaxel 135 mg/m2 day I, cisplatin 80 mg/m2 IV day I, and etoposide 50 mg/m2 IV day I, and 100 mg/m2 orally days 2 and 3, every 3 weeks. In the second group, the etoposide was increased to 80 mg/m2 IV day I and 160 mg/m2 orally days 2 and 3. In the third group, paclitaxel was increased to 175 mg/m2 IV day I. Granulocyte colony-stimulating factor was not given on the first cycle, but was given on subsequent cycles if grade 4 neutropenia developed. So far, 13 patients have been entered on the study; all are evaluable for toxicity and nine are evaluable for response. The major toxicity was neutropenia, with no other grade 4 toxicities observed. All patients received the full six cycles of therapy. Thus far, partial responses have been observed in four patients (44%) and complete responses in five patients (56%), for an overall response rate of 100%. This ongoing study has shown that full doses of each of these three active drugs can be administered safely on an outpatient basis. The encouraging early results should lead to a multicenter phase II evaluation of the PET combination.