Previous structural investigations performed on the lipopolysaccharides (LPSs) from the human gastric pathogen Helicobacter pylori have revealed that these cell surface glycan molecules express type 2 partially fucosylated, glucosylated, or galactosylated N-acetyllactosamine O antigen chains (O-chains) of various lengths, which may or may not be terminated at the nonreducing end by Lewis X (Le(x)) and/or Le(y) blood group epitopes in mimicry of human cell surface glycoconjugates and glycolipids, Subsequently, serological experiments with commercially available Lewis-specific monoclonal antibodies also have recognized the presence of Le(x) and Le(y) blood group antigens in LI, pylori but, in addition, have indicated the presence of type 1 chain Le(a), Le(b), and Le(d) (H-type 1) blood group epitopes in some H. pylori strains. To confirm their presence, structural studies and additional serological experiments mere undertaken on H., pylori strains suspected of carrying type 1 chain epitopes, These investigations revealed that the O chain region of H. pylori strain UA948 carried both Le(a) (type 1) and Le(x) (type 2) blood group determinants. The O-chain from H. pylori UA955 LPS expressed the terminal Lewis disaccharide (type 1 chain) and Le(x) and Le(y) antigens (type 2), The O-chain of H. pylori J223 LPS carried the type 1 chain precursor Le(c), the H-l epitope (Le(d), type 1 chain) and an elongated nonfucosylated type 2 N-acetyllactosamine chain (i antigen). Thus, O-chains from H., pylori LPSs can also express fucosylated type 1 sequences, and the LPS from a single H., pylori strain may carry O-chains with type 1 and 2 Lewis blood groups simultaneously. That monoclonal antibodies putatively specific for the Le(b) determinant can detect glycan substructures (Le disaccharide, Le(c), and Le(d)) of Le(b) indicates their nonspecificity. The expression of both type 1 and 2 Lewis antigens by H. pylori LPSs mimics the cell surface glycomolecules present in both the gastric superficial (which expresses mainly type 1 ...