The carbohydrate present on glycoprotein can influence their biologic and functional properties. In the present paper we have assessed the role of oligosaccharides in the polymerization and effector functions of IgG with the 18 amino acid extension of IgM added to its carboxy terminus (IgGmutp). We found that IgG1mutp and IgG3mutp lacking the carbohydrate addition site in C(H)2, in the tail-piece or both assembled into polymers as well as the glycosylated versions. Aglycosylated polymers retained the ability to activate complement as assayed by C1q binding and hemolysis, although they were not as effective as their wild type polymer counterparts. Although IgGmutp lacking the carbohydrate in the tail-piece was able to bind to FcgammaRII, completely aglycosylated polymers lost the ability to bind to both FcgammaRI and FcgammaRII, suggesting a critical role for the C(H)2 sugar in FcR binding. Absence of the mutp carbohydrate increased the half life of polymeric IgG1, whereas absence of the carbohydrate in C(H)2 accelerated the clearance rate.