While the ABO blood group, comprising the carbohydrate antigens H, A, and B, is the most well-known of the blood groups, various less prominent blood groups have also been described. Lewis a (Lea) and Lewis b (Leb) are carbohydrate antigens of one such group, Lewis blood group.1) Other carbohydrate antigens structurally related to these antigens include sialyl Lewis a (sLea), Lewis x (Lex), its sialylated derivative, sialyl Lewis x (sLex), and Lewis y (Ley).2,3) Lex is the epitope for SSEA1, an undifferentiated marker for mouse embryonic stem cells (ES cells).4) sLex is a ligand for the cell adhesion molecule E-selectin which is involved in the migration of neutrophils to sites of inflammation.5,6,7) Additionally, expression of Lex, Ley, sLea, and sLex is increased in cancers and is involved in cancer progression.3,8) Indeed, sLea (CA19-9) is used as a tumor marker. We have a wide selection of antibodies against such carbohydrate antigens.