N-glycans, O-glycans and glycolipids are frequently fucosylated at terminal sites. Therefore, fucose is often part of a sugar epitope with an important biological function. Well-known fucose-containing glycans include Lewis and ABO blood group antigens. Lewis epitopes are key elements involved in leukocyte homing and extravasation and thus are important for lymphocyte maturation and natural defense functions. Fucose-containing glycans also play critical roles in cell signaling and development. More than 10 fucosyltransferases have been cloned and all of them are Golgi-resident type II membrane proteins. 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 alpha (1-3) or alpha (1-4) fucosyltransferases and are responsible for Lewis antigen generation . FUT8 is the only alpha (1,6) fucosyltransferase that adds a fucose to the chitobiose core of N-glycans. The alpha 1,6-fucosylation of N-glycan in human IgG1 was reported to suppress antibody-dependent cellular cytotoxicity. Disruption of the FUT8 gene induced severe growth retardation, emphysema, and death during postnatal development in mice. The absence of alpha 1,6-fucosylation on transforming growth factor-beta 1 (TGF-beta 1) receptors was found to be involved in the mouse phenotypes. The activity of this enzyme has been measured using a phosphatase-coupled assay.