A receptor moiety and blood group substance recognized by the O75X adhesin was studied. Well-defined erythrocytes representing different blood group systems and bacterial derivatives carrying plasmid pBJN406 encoding the adhesin were used in a direct hemagglutination assay. We showed that Dr blood group antigen, a component of the IFC blood group complex, is the receptor for the O75X fimbrialike adhesin (Dr hemagglutinin) of uropathogenic Escherichia coli. The molecule recognized by the Dr hemagglutinin on Dr blood group substance is a chloramphenicol-like structure. The inhibitory effect of the active compounds indicates that a tyrosine-containing molecule could be a natural receptor for the Dr hemagglutinin. Dr blood group substance was found in tubular basement membrane and Bowman's capsule of the human kidney. Specific attachment of a Dr hemagglutinin-positive bacterial strain to the kidney substructures was inhibited by chloramphenicol.