BACKGROUND: Arsenic trioxide is highly active in patients with acute promyelocytic leukemia. There are also preclinical data to suggest that this drug might be active in nonhematopoietic malignancies, and transitional cell carcinoma cell lines are particularly sensitive to this agent. PATIENTS AND METHODS: Twelve evaluable patients with metastatic urothelial cancer were treated with arsenic trioxide in a phase II trial conducted by the Cancer and Leukemia Group B. Eligible patients were required to have measurable urothelial cancer and a maximum of 1 previous chemotherapy regimen. Arsenic trioxide was given at a dose of 0.3 mg/kg daily for 5 days every 28 days. RESULTS: No major responses were observed; 4 patients achieved stable disease. The median survival was 6.5 months (95% CI, 3.9-13.4 months). The most commonly observed toxicities included fatigue and malaise, anemia, nausea, emesis, and constipation. CONCLUSION: Arsenic trioxide at this dose and schedule does not have significant activity in previously treated urothelial cancer and has substantial toxicity in this patient population.