OUTLINE: This is a randomized, placebo-controlled, double-blind, multicenter study. Patients are stratified according to participating center, site of disease (colon vs rectum), disease stage (II vs III), age, adjuvant chemotherapy (yes vs no), and type of chemotherapy regimen (1 vs 2 vs 3 vs 4 vs 5). Within 3 months of surgical resection alone or completion of adjuvant radiotherapy and/or chemotherapy after surgical resection, patients are randomized to one of four treatment arms.