Methylation, periodate oxidation, and partial hydrolysis studies on the capsular polysaccharide, and on the carboxyl reduced polymer, of Klebsiella K21 show the structure to consist of a repeating unit.[Formula: see text]The anomeric linkages were determined by p.m.r. spectroscopy of isolated oligosaccharides and, in part, by specific enzymes. P.m.r. spectroscopy of the original polysaccharide in methyl sulfoxide-d6 showed clearly a ratio of one pyruvic acid ketal (CH3, τ 8.5) to five anomeric protons (τ 4.65–5.40).