Insulin-like growth factor (IGF-I) is a potent mitogen and an anti-apoptotic agent which is regulated by insulin-like growth factor binding protein-3 (IGFBP-3). IGFBP-3 carries IGF-I through the bloodstream to the target tissues and protects it from proteolytic degradation. IGFBP-3 reduces tumorigenic potential of colon cancer cells in vitro. IGFBP-3 may inhibit target cells directly. In the present study, we assessed whether serum levels of IGF-I and IGFBP-3 could be used as tumor markers in patients with colorectal cancers and evaluated its relationship with known tumor markers, carcinoembryogenic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9).