The structure of the capsular polysaccharide from Klebsiella type 57 has been investigated. Methylation analysis, uronic acid degradation, modified Smith degradation and graded acid hydrolysis were the principle methods used. Pure oligomeric fragments were isolated using the three methods of degradation and characterized by chemical and physical methods. These studies show the structure to consist of a tetrasaccharide repeating unit (all sugar residues have the D-configuration and are pyranosidic).