The most devastating aspect of cancer is the emergence of metastases. Thus, identification of potentially metastatic cells among a tumor cell population and the underlying molecular changes that switch cells to a metastatic state are among the most important issues in cancer biology. Here we show that, although normal human colonic epithelial cells lack the glycosphingolipid globotriaosylceramide (Gb3), this molecule is highly expressed in metastatic colon cancer. In addition, a subpopulation of cells that are greatly enriched in Gb3 and have an invasive phenotype was identified in human colon cancer cell lines. In epithelial cells in culture, Gb3 was necessary and sufficient for cell invasiveness. Transfection of Gb3 synthase, resulting in Gb3 expression in noncancerous polarized epithelial cells lacking endogenous Gb3, induced cell invasiveness. metastases ͉ invasion ͉ filopodia C olorectal cancer is the second leading cause of cancer death in the U.S. (1, 2). The high mortality associated with colorectal cancer is related to its ability to spread beyond the large intestine and to invade distant organs. One route to improve understanding of the molecular mechanisms of metastasis is by the identification of genes that are differently expressed during cancer progression and͞or are responsible for acquisition of the metastatic phenotype. Although many molecular factors have been identified as contributing to metastases and represent potential targets for treatment (3), much remains to be learned about the biology of the metastatic process. Aberrant glycosylation, which has been observed in essentially all types of human cancers during cancer progression into the metastatic stage, is an example of a metastases-related