OUTLINE: This is a randomized, placebo controlled study. Patients are stratified according to colorectal tumor (primary vs metastatic). Patients are randomized into one of two treatment arms. Arm I: Patients receive oral eniluracil twice daily on days -2 and -1 followed by surgical resection and tissue harvest on day 0. Arm II: Patients receive an oral placebo as in arm I followed by surgical resection and tissue harvest on day 0. Patients are followed weekly for 1 month.