We performed a phase I trial of 3-hour paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) (dose levels of 150, 175, 200, and 225 mg/m2) plus carboplatin dosed to an area under the concentration-time curve of 6. Sixteen patients were treated. Dose-limiting neuropathy was demonstrated in one patient each at the 175 and 200 mg/m2 dose levels. Grade 3 to 4 granulocytopenia was common; grade 3 to 4 thrombocytopenia was uncommon. The maximum tolerated dose of the regimen was not reached. Two complete and seven partial responses were demonstrated. We conclude that paclitaxel 225 mg/m2 plus carboplatin dosed to an area under the concentration-time curve of 6 can be administered to patients with advanced carcinoma of the urothelium. The regimen has encouraging preliminary activity. Phase II accrual is ongoing.