The chemical structure of the lipid A component of lipopolysaccharides from Chromobacterium violaceum NCTC9694 was studied. Sequential treatment of lipopolysaccharide with alkali, acid, sodium borohydride and hydrazine allowed the isolation of a reduced glucosamine disaccharide. According to methylation studies and enzymic analysis with beta-N-acetylglucosaminidase the D-glucosamine residues are beta(1 leads to 6) linked. The disaccharide carries two phosphate groups, one being linked glycosidically, the other being linked as an ester to the non-reducing glucosamine. Application of a different degradation pathway shows that the ester-bound phosphate group is substituted by a 4-aminoarabinosyl residue and that the glycosidically linked phosphate group is substituted by a glucosaminyl residue. Neither the amino nor the hydroxyl groups of both these substituents are acylated. This backbone structure is shown in the following formula: (formula: see text). The amino groups of the central glucosamine disaccharide are substituted by D-3-hydroxy-dodecanoic acid, the hydroxyl groups by dodecanoic, L-2-hydroxydodecanoic and D-3-hydroxy-decanoic acid.