A neutral O-polysaccharide liberated by mild acid hydrolysis of a lipopolysaccharide isolated from Azospirillum lipoferum SpBr17 was investigated using 1D and 2D (1)H and (13)C NMR spectroscopy, including HSQC, HMBC, and NOESY as well as SDS-PAGE electrophoresis along with sugar and methylation analyses. The structure of the O-specific polysaccharide repeating unit was established as follows: [Formula: see text]. The presented structure is a revised version of the formula that was published earlier in the Abstracts of the 9th International Congress on Nitrogen Fixation in Cancun (Mexico, 1992).