Fluoropyrimidine therapy for elderly colorectal cancer patients remains controversial. Tumoral levels of thymidine phosphorylase (TP), dihydropyrimidine dehydrogenase (DPD), and the ratio of TP to DPD determined by an enzyme-linked immunosorbent assay were compared between colorectal cancer patients aged 75 or over (elderly group, n = 25) and those 74 years or less (control group, n = 87), in order to examine the characteristics of colorectal cancers in the elderly from the viewpoint of metabolic and anabolic pathways of fluoropyrimidines. The level of TP was 78.4 +/- 47.0 unit/mg protein in the elderly group and 82.4 +/- 70.9 unit/mg protein in the control group (p = 0.86). The level of DPD was 53.7 +/- 43.1 unit/mg protein in the elderly group and 52.6 +/- 37.7 unit/mg protein in the control group (p = 0.73). The ratio of TP to DPD was 2.0 +/- 1.2 in the elderly group and 1.8 +/- 0.9 in the control group (p = 0.44). These three parameters did not differ between the groups when divided according to Dukes' stage (Dukes' A.B versus Dukes' C.D). These results suggest that there are no age-specific characteristics in relation to conversion of fluoropyrimidines such as capecitabine and doxifluridine to 5-fluorouracil (FU) and degradation of 5-FU in colorectal cancers.