The title compound (PE-Kdo) was isolated after hydrolysis of the lipopolysaccharides of Escherichia coli K-12 strain W3100 and Salmonella minnesota strains R4 and R7, and the location of the 2-aminoethyl phosphate group at position 7 was established by 13C-n.m.r. spectroscopy. Derivatives of PE-Kdo were acetylated, silylated, and methylated in order to evaluate their usefulness for analysis by g.l.c.-m.s.