The O-chain polysaccharide of the lipopolysaccharide of Xanthomonas campestris pv. manihotis strains GSPB 2755 and GSPB 2364 was studied by sugar and methylation analyses and 1 H and 1 3 C NMR spectroscopy, including 2D COSY, TOCSY, NOESY, and H-detected 1 H, 1 3 C heteronuclear multiple-quantum coherence (HMQC) experiments. The polysaccharide was found to contain l-rhamnose and l-xylose in the ratio 3:1, and the following structure of the tetrasaccharide repeating unit was established: