Adjuvant chemotherapy has been shown to alter the natural history of resected colon cancer. Two regimens (fluorouracil [5-FU] plus leucovorin and 5-FU plus levamisole) have been found to prolong disease-free survival and overall survival in affected patients. Previous comparisons of these two regimens indicate that 5-FU plus leucovorin may offer a small disease-free survival and overall survival advantage. Evidence that UFT (uracil and tegafur) plus oral leucovorin is associated with significant antitumor activity and has an acceptable toxicity profile makes this a logical formulation for the adjuvant treatment of colon cancer. The National Surgical Adjuvant Breast and Bowel Project Protocol C-06 is a randomized comparison of the relative efficacies of 5-FU plus leucovorin vs UFT plus leucovorin. Preliminary analysis of the toxicity findings among 1,530 evaluable patients indicates that both regimens are well tolerated and have similar toxicity profiles.