A phosphorus-containing polysaccharide has been isolated from defatted cells of Actinoplanes sp. INA 3697. The structure of the polymer has been established by a non-destructive method including one- and two-dimensional NMR 1H-spectroscopy as well as by NMR 13C-spectroscopy and confirmed by chemical analysis of the monosaccharide composition and the repeating link. Association of the repeating units-2-acetamido-2-deoxy-beta-D-mannopyranosyl-(1-->3)-2-acetamido -2-deoxy-D-glucopyranoses, is provided by phosphodiester bonds between C1 of N-acetylglucosamine and C6 of N-acetylmannosamine. The polymer molecule is made up of about 12 disaccharides and is localized in the cell wall of the actinomycete. No structurally identical phosphorylated polysaccharides have as yet been found in prokaryotes.