The structures I and II were established for the O-antigens of Pseudomonas solanacearum ICMP 7942 and ICMP 8169, respectively, by means of NMR-spectroscopy, including 2D homonuclear shift-correlated spectroscopy (COSY), rotating-frame NOE spectroscopy (ROESY) and heteronuclear 13C, 1H multiquantum correlation spectroscopy (HMQC). In the polysaccharide of the ICMP 8169 strain substitution of the main chain by the xylose residue is non-stoichiometric, i.e. this antigen contains also the repeating units of the polysaccharide of the ICMP 7942 strain (the ratio II: I is approximately 3:1). [formula: see text]