Twenty-six patients with advanced colorectal cancer were treated with UFT and leucovorin (LV). On day 1, patients received LV 500 mg/m2 in IV infusion, followed by 15 mg/12 h for 13 days. On days 1 to 14, patients took oral UFT twice daily. Three cycles were given every 28 days, unless grade III-IV toxicity appeared. The initial dose of UFT (200 mg/day) was increased until 800 mg/day. Dose limiting toxicities were stomatitis, diarrhea and epigastralgia. The maximum tolerated dose of UFT was 390 +/- 10 mg/m2. Three out of 24 evaluable patients achieved a partial response and 1 a complete response with UFT doses of 260 to 390 mg/m2. These results warrant confirmation in phase II studies.