A study by Etienne et al has raised questions regarding the utility of DPD activity alone to predict patients at risk for fluoropyrimidine toxicity. They prospectively studied 185 patients treated with 5FU containing chemotherapy regimens. They found a normal distribution of DPD activity with a mean value of 0.222 nmol/min/mg protein. They did not find any correlation between DPD activity and 5FU toxicity. The researchers propose to study the effect of these two polymorphic enzymes on 5FU/LV's toxicity in adjuvant colon cancer patients. The researchers anticipate that patients homozygous for 2R/2R will have higher rates of overall toxicity, diarrhea, neutropenia and mucositis than 3R/3R homozygotes. For MTHFR, the researchers anticipate that TT homozygotes will have higher rates of overall toxicity, diarrhea, neutropenia, and mucositis than CC homozygotes. The effect of MTHFR polymorphism on 5FU/LV's toxicity will be examined controlling for thymidylate synthase genotype.