Lipopolysaccharides (LPS) have been isolated from the cells of phytopathogenic bacteria Burkholderia (Pseudomonas) solanacearum strains (representatives of I, II and IV biovars) using mild acid hydrolysis followed by gel permeation chromatography of carbohydrate residues on Sephadex G-50 to yield five O-specific polysaccharides (O-PS). The O-PS structures were established by 13C-NMR spectroscopy. It has been found that O-PS have a linear or branched structure. The former represents a tetrasaccharide comprising three L-rhamnose residues and one N-acetylglucosamine residue. The differences between the strains are in the configuration (alpha or beta) and type [(1 --> 2) or (1 --> 3)] of the link between D-GtcpNAc and L-Rhap. The branched structure represents a xylosylated version of the linear structure and consists of pentasaccharide repeating units. The bacterial strains under study may be represented by multiple structural types, O-PS, involving both linear and branched repeating units. There is no correlation between the O-PS structure and strain specificity for any particular plant host.