The main objectives of this phase II study were to determine efficacy and safety of the combination of UFT with Leucovorin and mitomycin C in patients with metastatic colorectal cancer. Ninety-seven patients were treated with UFT (91 patients 300 mg/m2, 6 patients 250 mg/m2) + Leucovorin 90 mg days 1-28 q 5 weeks. During the first 4 cycles the patients also received mitomycin C 7 mg/m2 on day 1. At the end of 4 courses patients with benefit from the treatment could receive further courses of UFT and Leucovorin alone. Two patients had a complete response (2%), 20 (21%) had a partial response, 40 (41%) had no change, 19 (20%) had progression, and 16 (17%) were not evaluable for response. The overall response rate by intention to treat was 22/97 (23%). Median time to progression was 5 months and median survival 13 months. Severe (grade 3-4) toxicities included: anorexia 3%, nausea 6%, vomiting 7%, diarrhoea 7%, and fatigue 9%. Febrile neutropenia, renal failure, and thrombocytopenia were seen in 1% of the patients, respectively. The combination of UFT with Leucovorin and mitomycin C shows similar clinical activity with regard to overall response rate (23%) and survival (13 months) to other frontline 5-fluorouracil-based therapies in metastatic colorectal cancer patients. The results indicate that mitomycin C did not increase either efficacy or toxicity. Therefore, phase III trials with this regimen cannot be recommended.