Human galactoside 3(4)-L-fucosyltransferase (FUT3) may be involved in Lewis blood group (Le) determination. Le+ individuals have an active enzyme while Le- individuals have an inactive enzyme. FUT3 catalyses alpha-1,3 and alpha-1,4 glycosidic linkages involved in the expression of Le blood groups. The 1,3-galactosyl derivative is shown here (Cameron et al. 1995).