The structures of two bacterial antigens, one a capsular polysaccharide from Klebsiella K66 and the other a lipopolysaccharide from Escherichia coli 0:6, have been determined, using specific degradations and spectrochemical studies. Two glycosidation methods are described. One is the synthesis of 1,2-trans-linked aryl glycosides using fully acetylated glycopyranosyl bromides. The other is the synthesis of a-D-gluco- and a-D-galacto-pyranosides starting from fully benzylated a-D-glu- co-and a-D-galacto-pyranosyl chlorides. A novel reagent system for displacement of hydroxy groups in carbohydrates by iodine is presented. This reaction proceeds with inversion of configuration.