GM(3)-trisaccharide [Neu5Ac alpha-(2-->3)-Gal beta-(1-->4)-Glc beta-(1-->OR)] was synthesized using our ''active-latent'' thioglycosylation strategy. The trisaccharide was prepared with a p-acrylamidophenyl aglycon for copolymerization with acrylamide. The resulting water-soluble sialyl alpha-(2-->3)-lactoside copolyacrylamide with different carbohydrate incorporation was shown to possess antigenic properties. Copyright (C) 1996 Elsevier Science Ltd