Background: Matrix metalloproteinases (MMPs), especially MMP-2 and MMP-9, play an important role in tumor invasion and metastasis. This study aimed to determine the serum levels of MMP-2, MMP-9, 130-and 225-kDa gelatinolytic bands and conventional tumor markers, carcinoembryonic antigen (CEA) and cancer antigen (CA) 19-9, in patients with gastrointestinal cancers. The relationship between these parameters and clinicopathological factors was also studied. Methods: Sera from controls (ns19), and patients with colorectal (ns47) and gastric (ns34) cancer were collected prospectively. The gelatinolytic activities of MMP-2, MMP-9, 130-and 225-kDa bands were determined using gelatin zymography. CEA and CA 19-9 were determined using immunoradiometric assay (IRMA). Results: Serum levels of MMP-9, 130-and 225-kDa gelatinolytic bands, CEA, and CA 19-9, but not MMP-2, in colorectal and gastric cancer were significantly higher than that of controls. No significant correlation was found between histological grade or clinical stage and levels of MMP-9, 130-and 225-kDa gelatinolytic bands, which were correlated (rs0.61-0.89, p-0.005). Conclusions: Our findings suggest that zymographic determination of