The purpose of this study was to examine the relation between tumoral expression of dihydropyrimidine dehydrogenase (DPD), the rate limiting enzyme of the degradation pathway 5-fluorouracil (5-FU), and the efficacy of 5-FU based chemotherapy for colorectal cancer. Twenty-eight colorectal cancer patients who had underwent noncurative resection (n = 16) or had developed recurrence (n = 12) were enrolled. All patients were given 5-FU plus leucovorin intravenously and UFT (1 M Tegafur, 4 M Uracil) perorally. The expression levels of the DPD in the primary lesions were determined by the enzyme-linked immunosorbent assay. Group A (n = 10) consisted of one patient with complete response, 4 with partial response, and 5 with no change (time to disease progression (TTP) > = 90 days). Group B (n = 18) consisted of 14 patients with progressive disease and 4 with NC (time to progression, < 90 days). The tumoral DPD levels did not differ between the groups (p = 0.58). There were no effective cases (n = 6) whose tumoral DPD levels were equal to or more than 83.2 U/mg protein (high DPD expression). There were marked overlaps in the DPD levels between the two groups whose DPD levels were less than 83.0 U/mg protein (moderate or low expression). These results suggest that high expression of tumoral DPD would be predictive to failure of fluoropyrimidine-based treatment. However, it is unlikely to set the optimal cutoff value for predicting the efficacy of this type of chemotherapy.