To further the understanding of the chemical basis for serological differentiation, the structural investigation of capsular polysaccharides, produced by the various Escherichia coli (E. coli) strains has been embarked upon in this and other laboratories. The structural elucidation of E. coli K34 capsular polysaccharide and related studies are reported in this communication. N.m.r. spectroscopy and sugar analysis data on E. coli K34 capsular polysaccharide indicated that it consists of a pentasaccharide repeating unit with glucose, galactose and glucuronic acid as its sugar components. The nature of the anomeric linkages was established by ¹H-n.m.r. spectroscopy and confirmed by the results of oxidation of the fully acetylated polysaccharide with chromic acid. Methylation, periodate oxidation - Smith hydrolysis and uronic acid degradation studies on the capsular polysaccharide and on the carboxyl reduced polymer, of E. coli K34 show the structure to consist of a repeating unit, [See Thesis for Diagram] All the sugar residues in this capsular polysaccharide were assigned the D-configuration from circular dichroism measurements. The D configuration of the α-glucose was confirmed by treatment of E. coli K34 bacteriophage generated oligosaccharide with α-D-glucosidase. From the results of the cross-reaction between E. coli K34 and other group 09 E. coli strains (K28, K31, K32 and K33), we suggest that the immunodominant sugar of E. coli K34 capsular polysaccharide may either be 1 → 2 linked glucuronic acid or the terminal glucose. The occurrence of 1 → 2 linked glucuronic acid in E. coli K34 polysaccharide is the first to be reported in bacterial polysaccharide. In this study E. coli K34 and K31 capsular polysaccharides were depolymerized using their corresponding bacteriophages. Characterization of the bacteriophage generated oligosaccharides revealed that the E. coli K34 and K31 bacteriophage-borne glycanases are galactosidase and glucosidase respectively.