BACKGROUND UFT is a fixed-ratio combination of uracil and Ftorafur, a prodrug that is absorbed orally and metabolized in vivo to 5-fluorouracil (5-FU). Uracil potentiates 5-FU through interference with its catabolism. The combination of UFT and leucovorin in patients with advanced incurable colorectal cancer, to evaluate preliminary activity and toxicity in this patient population. METHODS Twenty-one patients were treated. Twenty patients were evaluable for toxicity and response. Patients received UFT 350 mg/m2/day divided every 8 hours. Patients took a 5 mg tablet of leucovorin every 8 hours, concurrent with each UFT dose. Treatment was continued for 28 consecutive days, followed by a 7-day rest. RESULTS Five major objective responses (one complete and four partial) were observed. Toxicity was mild, with no dose-limiting myelosuppression. Four patients experienced grade 3 diarrhea or higher, and two patients experienced dose-limiting mucositis. CONCLUSIONS UFT and low dose leucovorin is a well tolerated, orally administered regimen with activity in colorectal cancer. A randomized comparison of this regimen with conventional parenteral regimens is warranted.