Vinblastine sulfate 0.10-0.15 mg/kg IV every week, was given to 37 patients with bidimensionally measurable, metastatic transitional cell carcinoma of the urothelial tract. Twenty-eight patients, the majority of whom had received extensive prior chemotherapy, had an adequate trial and five (18%; 95% confidence limits, 3-33%) achieved a partial remission (greater than 50% decrease in tumor size) of 2-5 months' duration. Responding sites included lung and nodal metastases. Toxicity, primarily leukopenia, was mild to moderate. The 18% response rate obtained in heavily pretreated cases suggests that vinblastine sulfate has some efficacy in the treatment of patients with advanced urothelial tract tumors.