From a Shigella sonnei R mutant which incorporates into its cell wall lipopolysaccharide D-glycero-D-mannoheptose and contains no L-glycero-D-mannoheptose, a nucleotide-linked sugar was isolated and identified as adenosine 5'-diphosphate-D-glycero-d-mannoheptose by chemical and chromatographic analysis. This intermediary compound is assumed to play a role in heptose biosynthesis of Enterobacteria.