Neoplastic transformation is often associated with characteristic changes in the expression of the sialyl Lewisa and sialyl Lewisx antigens, representing typical tumor-associated carbohydrate antigens. High amounts of sialyl Lewisa are present in human adenocarcinomas of the colon, pancreas and stomach. A growing amount of data suggests that this carbohydrate structure is the ligand for E-selectin. Sialylated Lewis structures present on the surface of tumor cells are carried by the carbohydrate chains of glycoproteins and glycolipids. There are several lines of evidence showing that sialyl Lewisa is responsible for the adhesion of human cancer cells to endothelium. E-selectin present on endothelial cells mediates these interactions. Selectins and their carbohydrate ligands can thus play an important role in the selective homing of tumor cells during metastasis. However, the presence of sialyl Lewisa antigen on the surface of tumor cells and their adhesion to E-selectin-expressing cells in in vitro adhesion assay by itself can not be directly related to metastatic properties of all cancer cells.