Because N-, O-glycans and glycolipids are frequently fucosylated at terminal sites, fucose is often found to be essential for sugar epitope and lectin ligand generation. Well-known fucose containing structures include Lewis structures and ABO blood group antigens. Lewis structures are key elements involved in leukocyte homing and extravasation process and thus are essential for lymphocyte maturation and natural defense functions. Fucose containing glycans also play essential roles in cell signaling and development. So far, more than 10 fucosyltransferases have been cloned from the human genome. FUT1 and FUT2 are alpha 1-2 fucosyltransferases and are responsible for ABO blood group antigen synthesis. FUT3, FUT4, FUT5, FUT6, FUT7 and FUT9 are responsible for Lewis structure generation through their alpha 1-3 or alpha 1-4 fucosyltransferases activities. FUT3, also known as Lewis blood group fucosyltransferase, is unique by having both strong alpha 1-3 and alpha 1-4 fucosyltransferase activities. FUT3 has high homology with FUT5 and FUT6 due to gene duplication. FUT7 is exclusively responsible for biosynthesis of sialyl Lewis X epitope in leukocytes and high endothelial venule cells. FUT8 is an alpha 1-6 fucosyltransferase that adds a fucose to the chitobiose core of N-glycans. Predicted as type II transmembrane proteins and Golgi enzymes, some of the fucosyltransferases can also be found in plasma. R&D Systems rhFUTs correspond to the luminal domains.