Dihydropyrimidine dehydrogenase (DPD) is the first and rate-limiting enzyme in the catabolism of 5-fluorouracil (5-FU). DPD activity in tumor tissue may consequently serve as a predictive factor for sensitivity to 5-FU. The purpose of this study was to elucidate the stability of DPD activity over time in resected colorectal cancer tissue. DPD activity was measured in samples frozen immediately after the tumor was resected and in samples that had been allowed to stand at room temperature for 15, 30, 60, 120, and 180 min before being frozen. Surgical specimens obtained from 15 cases with advanced colorectal cancer were analyzed. The effects of differences among individuals and differences in time between collection and freezing were assessed by two-way analysis of variance (ANOVA). Significant differences in DPD activity were found among tumors (p=0.001), but there were no significant differences in the same tumor depending on the time between collection and freezing (p=0.496). Based on these results, it appears possible to make comparative assessments of DPD activity in colorectal cancer tissue without strictly stipulating the time between resection and freezing.