Background: Bladder cancer is a chemosensitive tumour, however, there is no effective therapy for patients with metastatic disease who failed to respond or relapsed after prior treatment with cisplatin-based chemotherapy. Single agent 5-fluorouracil has modest activity in bladder cancer. The combination of 5-fluorouracil with folinic acid results in stabilization of the ternary complex of 5-fluorodeoxyuridine monophosphate-thymidylate synthetase-5,10 methylene tetrahydrofolate leading to increased DNA inhibition and increased cytotoxicity of 5-fluorouracil. Patients and methods: Fourteen evaluable patients with metastatic bladder cancer were treated with 5-fluorouracil at 300 mg/m(2) and folinic acid at 200 mg/m(2) daily for five days. Results: There were no complete or partial responses. One patient had a minor response and three patients had stable disease. Diarrhea and mucositis occurred in 25% of patients. There was one treatment-related death. Conclusion: High dose folinic acid did not increase the cytotoxicity of 5-fluorouracil in metastatic bladder cancer after cisplatin failure.