Phosphoglucose isomerase (PGI) is a ubiquitous cytosolic enzyme that plays a key role in glycolysis. PGI is also a multifunctional protein that acts in the extracellular milieu as a potent mitogen/cytokine. Increased expression of PGI and its receptor has been found in a wide spectrum of malignancies and is associated with cancer progression and metastasis. In this study, the role of PGI in the growth and metastasis of colon cancer cells was determined. To elucidate the functional role of PGI in colorectal cancer, we stably transfected PGI cDNA into human colon cancer cells. We used an orthotopic mouse tumor model to assess whether overexpression of PGI enhances liver metastasis. Overexpression of PGI stimulated the in vitro invasion of DLD-1 cells. In vivo, after orthotopic implantation into the cecum of nude mice, parental and empty vector-transfected DLD-1 cells produced small tumors without liver metastasis, whereas PGI-overexpressing DLD-1 cells produced large tumors and liver metastases. In conclusion, overexpression of PGI significantly contributes to the aggressive phenotype of human colon cancer and, thus, may provide a novel therapeutic target.