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This thesis describes chemical synthesis of carbohydrates and glycopeptides useful in studies of biologically interesting systems. The following topics are addressed: [Papers I-IV and supporting information]: [I] The non-reducing end di- and trisaccharide structures of an erythrocyte glycolipid responsible for the rare NOR polyagglutination were chemically synthesized. The syntheses were based on a -D-Galp-(14)--D-GalpNAc-(1) structural element found only recently in Nature, and derivatives thereof have not been synthesized before. Both the synthesized oligosaccharides specifically inhibited human anti-NOR antibodies, with the trisaccharide being 300 times more active than the disaccharide. [II] Derivatives of lactose with the galactose ring substituents replaced by 2´, 3´, 4 ´ and 6´ deoxy and 3 ´ acylamino functions were prepared. The lactosyl derivatives were tested as acceptors for the Neisseria menigitidis N-acetylglucosaminyltransferase catalyzed -(13) glycosylation reaction, using UDP-GlcNAc as donor. The 6´-deoxy compound showed nearly a threefold increase in activity compared with the reference substance phenyl -lactoside, whereas the 2 ´ and 4´-deoxy derivatives were less active. The 3´-deoxy and 3´