Sialosyl-Lea and sialosyl-Lex are tumor-associated carbohydrate antigens present in different types of human tumors. They are commonly found on the cell surface of a variety of adenocarcinomas such as lung cancer, gastric cancer, pancreatic cancer and colorectal cancer, and in serum of cancer patients. Both antigens have been proposed as important diagnostic markers and they are used in detecting and monitoring of these diseases. Recently, it has been shown that sialosyl-Lea and sialosyl-Lex carbohydrate structures are ligands for selectins, newly described family of adhesion molecules. Selectins function as lymphocyte-homing and leukocyte enrollment receptors, or as activation dependent cell surface receptors of platelets and endothelial cells. Several lines of evidence suggest that sialosyl-Lea and sialosyl-Lex are responsible for adhesion of human cancer cells to endothelium. It has been shown that E-selectin and P-selectin present on endothelial cells mediate these interactions. The mentioned facts suggest that selectins and their carbohydrate ligands can play an important role in a selective homing of tumor cells during metastasis.