We conducted a phase II trial in chemotherapy-naive patients with advanced non-small cell lung cancer to determine the efficacy of paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) delivered at a maximum tolerated dose of 175 mg/m2 on an extended weekly schedule. Patients with stage IIIB/IV non-small cell lung cancer were eligible if they had an Eastern Cooperative Oncology Group performance status of 0 to 2, had received no previous chemotherapy, demonstrated normal hematologic and hepatic function, and could provide informed consent. Paclitaxel 175 mg/m2 was administered as an intravenous infusion weekly over 3 hours with standard premedication, for 6 weeks of an 8-week cycle. Doses were modified for absolute neutrophil count less than 1.5 x 10(9)/L or neuropathy greater than grade I on the day of therapy. Patients without progressive disease received subsequent cycles at the same dose. To date, 30 patients have been enrolled; data are available for 25. The median age was 65 years (range, 38 to 78 years), 23 patients were performance status 0 or 1, and 14 had received prior radiation. Sites of disease included the lung (23 patients), central nervous system (11), bone (seven), liver (one), kidney (one), and soft tissue (eight). Eighty-three percent, 75%, 58%, and 50% of intended doses were delivered during cycles 1 though 4, respectively. Grade 2/3 neuropathy occurred in nine patients, but improved in all nine following dose reduction. Grade 3/4 neutropenia occurred in 10 patients. Partial responses occurred in 14 of 25 patients (56%; 95% confidence interval, 46% to 66%). Median duration of response was 6.5 months, and the 1-year survival rate was 53%. The extended weekly paclitaxel schedule results in enhanced dose intensity, marked activity, and acceptable toxicity. Paclitaxel given weekly at maximum dose intensity may be more effective than conventional paclitaxel administration schedules.