Helicobacter pylori is a microaerophilic bacterium found in the stomach of asymptomatic humans as well as patients with acid peptic disease and gastric adenocarcinoma. We have developed an in situ adherence assay to examine the cell lineage-specific nature of binding of this organism and to characterize the nature of cell surface receptors that recognize its adhesin. Fluorescein isothiocyanate-labeled H. pylori strains were bound to surface mucous cells present in the pit region of human and rat gastric units but not to mucous neck, parietal, or chief cell lineages present in the glandular domains of these units. Binding was abolished by proteinase K treatment of tissue sections and by pretreatment of the bacteria with bovine submaxillary gland mucin, a rich source of fucosylated and sialylated carbohydrates. Several lines of evidence suggest that binding to surface mucous cells is not dependent upon terminal nonsubstituted alpha 2,3- and alpha 2,6-linked sialic acids in the adhesin receptor: (i) binding was not inhibited by incubating H. pylori strains with sialylated glycoconjugates such as fetuin and free sialyllactose; (ii) immunohistochemical stainings using the sialic acid-specific Sambucus nigra and Maackia amurensis lectins and the cholera toxin B subunit did not detect any sialylated glycoconjugates in these epithelial cells; and (iii) binding was not sensitive to metaperiodate under conditions that selectively cleaved carbons 8 and 9 of terminal nonmodified sialic acids. A role for fucosylated epitopes in the glycoprotein(s) that mediate binding of H. pylori to surface mucous cells was suggested by the facts that this lineage coexpresses the adhesin receptor and major fucosylated histo-blood group antigens, that monoclonal antibodies specific for histo-blood group antigens H, B, and Leb block binding, and that the lectin Ulex europaeus type 1 agglutinin, which is specific for alpha-L-fucose, also bound to the same cells that bound the bacteria. Furthermore, human colostrum secretory IgA inhibited adhesion in a metaperiodate- and alpha-L-fucosidase-sensitive but neuraminidase-independent fashion. The in situ adherence assay should be useful in further characterizing the H. pylori adhesin and its receptor and for identifying therapeutically useful compounds that inhibit strain-specific and cell lineage-specific binding of this human pathogen.