OBJECTIVES: I. Determine the enzymatic activity of dihydropyrimidine dehydrogenase (DPD) in peripheral blood mononuclear cells (PBMC), normal mucosa, or normal liver in patients with primary or metastatic colorectal cancer. II. Evaluate the ability of eniluracil to inactivate DPD in the tumor, PBMCs, and normal tissue in this patient population. III. Assess DPD recovery and uracil levels in PBMCs following surgical resection in these patients.