A Phase I-II trial of gallium nitrate was conducted in 40 patients with bidimensionally measurable urothelial tract tumors who had failed to respond to combination chemotherapy with methotrexate, vinblastine, doxorubicin, and cisplatin. Partial responses were observed in 4 of 23 patients (17.4%) who received 350 mg/m2/d or more for 5 days by continuous intravenous infusion. In two additional patients who received 350 mg/m2/d or more, a minor response and a mixed response were observed. The median duration of response was 4 months (range, 2 to 8 months). A dose-response relationship was suggested because no responses were observed in 17 patients who received less than 350 mg/m2/d. Myelosuppression was minimal. The dose-limiting toxic reaction was a reversible optic neuropathy that occurred in 3 of 11 patients who received 400 mg/m2/d. Further evaluation of infusional gallium nitrate is warranted in patients with urothelial tract malignant tumors.