Lipopolysaccharides (LPS) from phenol-water extraction of dyspeptic (P466) and asymptomatic (MO19) strains of Helicobacter pylori were each isolated as water-soluble material of high relative molecular mass (high M(r)) and as water-insoluble gels of low M(r). Chemical and spectroscopic analyses of the soluble LPS and oligosaccharides liberated from the water-insoluble gels led to proposed structures for chains comprising the O antigen, intervening, and core regions. As in the LPS from the type strain NCTC 11637 [Aspinall, G. O., et al. (1996) Biochemistry 35, 2489-2497], the O antigen region of the P466 LPS is characterized by the presence of extended chains with fucosylated and nonfucosylated N-acetyllactosamine units, the former carrying alpha-L-fucopyranose units at O-3 of beta-D-GlcNAc residues. This structure differs from that of the type strain in termination of the O chain by a Lewis(y) (Le(y)) antigenic determinant [alpha-L-Fuc(1-->2)beta-D-Gal(1-->4)[alpha-L-Fuc(1-->3)]beta-D-GlcNAc] but also has internal Lewis(x) (Le(x)) units. The inner core region of the P466 LPS is indistinguishable from that in the type strain. In contrast, the O antigen region of the LPS from strain MO19 consists of a single Le(y) epitope linked via a 3-linked beta-D-Gal to an intervening region on the basis of a sequence of 3-linked D-glycero-alpha-D-manno-heptose residues which is in turn linked to an inner core identical to that in the type strain and the P466 strain. Results in this and the preceding paper show that LPS from the three H. pylori strains display molecular mimicry of human cell surface glycoconjugates but may vary in the expression of Le(x) or Le(y) determinants, the degree of O antigen chain extension, or in the presence of an additional region between the inner core and the O antigen.