Lipopolysaccharides were isolated from dehydrated Helicobacter pylori cells by the phenol-chloroform-petroleum ether and hot phenol/water extraction techniques. Biochemical characterization of the crude extracts indicated the following: The primary fatty acids and approximate molar ratios were 3-hydroxyoctadecanoic (2), 3-hydroxyhexadecanoic (1), and octadecanoic (1) acids. Lesser amounts of tetradecanoic, hexadecanoic, and octadecenoic acids were noted. 3-Hydroxytetradecanoic acid was not detected in either extract. Neutral sugar analyses detected glucose, galactose, two heptose isomers, and an unidentified deoxy-hexose. Glucosamine and glucosamine phosphate were the only amino sugars found in significant quantities. Analyses of other components included ethanolamine, phosphate, and protein. 3-Deoxy-D-manno-octulosonic acid (KDO) was detected, but in lower concentrations than would be expected in comparable enterobacterial lipopolysaccharides.