47 patients with advanced urothelial cancer and no prior chemotherapy were randomly assigned to therapy with either carboplatin or iproplatin. Both platinum analogues were administered intravenously every 28 days at doses of 400 mg/m2 carboplatin and 300 mg/m2 iproplatin. None of 14 evaluable patients treated with carboplatin responded. Therefore, this arm was closed and from then on all eligible patients were registered on the iproplatin arm. 5 of 29 evaluable patients treated with iproplatin achieved a partial response (17%) for a median duration of 27 weeks (range 22-37). Iproplatin did not induce renal function disturbance. Gastrointestinal toxicity was mild to moderate. Bone marrow toxicity predominantly consisted of thrombocytopenia and required platelet transfusions in 13% of patients. 2 patients developed hypersensitivity reactions. It is concluded that the bone marrow toxicity and the chance of hypersensitivity render iproplatin an unattractive alternative to cisplatin.