['It is important to seek the appropriate chemotherapy drugs to effectively eliminate colorectal cancers. To avoid unnecessary medication and uncomfortable side effects, it is important to estimate the chemosensitivity of cancers to 5-fluorouracil (5-FU) before chemotherapy.', 'We examined thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) gene expressions in 23 colorectal cancers, using quantitative reverse transcription-polymerase chain reaction (RT-PCR). We then evaluated the relationship between TS and DPD gene expression levels and the sensitivity of colorectal cancers to 5-FU, as determined by histoculture drug response assay (HDRA).', 'A significant increase in the TS expression score was observed in 5-FU-sensitive colorectal cancers (0.57 +/- 0.19) compared to 5-FU-resistant ones (1.16 +/- 0.98; P = 0.029), whereas no significant differences in DPD expression scores were observed in 5-FU-sensitive colorectal cancers (0.86 +/- 1.19) compared to 5-FU-resistant ones (0.56 +/- 1.05; P = 0.603).'] Is expression level of thymidylate synthase a good predictor of chemosensitivity to 5-fluorouracil in colorectal cancer?