Dihydropyrimidine dehydrogenase (DPD) and thymidylate synthase (TS) gene expressions in metastatic colorectal cancer have been reported to be predictive parameters for the efficacy of fluoropyrimidine-based chemotherapy. In this study, we investigated the association between both DPD and TS expressions in primary colorectal tumor and the antitumor effect in patients with metastatic colorectal cancer when treated with a fluoropyrimidine-based protocol. DPD and TS expressions were measured by reverse transcription-PCR in surgically resected materials of primary colorectal tumors from 37 patients who went on to receive oral treatment of uracil and tegafur and leucovorin for either synchronous or metachronous metastatic diseases. Relative mRNA amounts of DPD or TS were expressed as the ratios of targeted gene to glyceraldehyde-3-phosphate dehydrogenase reverse transcription-PCR products. Median values of DPD mRNA expressions were 0.30 and 0.65 for responding tumors and nonresponding ones, respectively, with a statistical significance (P < 0.0001). No responding tumor had a DPD mRNA expression >/= 0.5. A total of 19 tumors had low DPD mRNA expressions of <0.5, and 63% of them showed response. There was no responding tumor with both high DPD and high TS (TS mRNA expression >/= 1.0). However, the response rate was 75% in tumors with both low DPD and low TS. The median survival time was 16.3 months in patients with both low DPD and low TS versus 8.4 months in patients with high DPD or high TS mRNA expression. In conclusion, the combination of DPD and TS mRNA expressions in the primary tumor might be useful as predictive parameters for the efficacy of fluoropyrimidine-based chemotherapy for metastatic colorectal cancer.