In the main fraction of oligosaccharides obtained after the acetic acid hydrolysis of the lipopolysaccharides of the strain PM were identified: terminal bound glucose and L-glycero-D-manno-heptose, 1,2-,1,3,4-, and 1,3,4,6,-linked heptose. The oligosaccharide of the strain 1297 S contains terminal linked galactose, 1,4- or 1,6-linked glucose and 1,4-linked N-acetylglucosamine additionally. The molar ratios of these elements show the heterogenicity of the preparations. The determined molecular weights underline the R-character of the LPS. In the by-fractions of the acetic acid hydrolysis the known mannan and another polysaccharide with galactose and glucosamine were identified.