A major limitation to the application of therapeutic monoclonal antibodies is their reduced in vivo efficacy compared to their high efficacy as measured in vitro.Recent studies have shown that the presence of high amounts of multispecific endogenous serum IgG impairs the antibody-dependent cellular cytotoxicity (ADCC) of therapeutic antibodies in vivo by competing for binding to FcgammaRⅢ expressed on effector cells.Furthermore, studies have indicated that effector cells expressing the FcgammaRⅢ 1 58V/V phenotype (60% of the population) have a reduced affinity to therapeutic IgG in comparison to the FcgammaRⅢ 158F/F phenotype.Modification of the glycosylation moieties attached to the Fc part of the antibody, i.e.the absence of the core-fucose moiety at position Asn297, strongly enhances binding affinity to FcgammaRⅢ of both phenotypes.Glyco-engineering of therapeutic antibodies represents a promising approach to enhance their in vivo efficacy and in consequence to reduce dosage and production costs.