In this study, we raised monoclonal antibodies (MAbs) against three conserved Helicobacter pylori antigens, i.e., the N-acetylneuraminyllactose-binding fibrillar hemagglutinin, HpaA; the flagellin subunits, FlaA and FlaB; and a species-specific 26-kDa protein. The MAbs were used for the development of sensitive inhibition enzyme-linked immunosorbent assays for quantification of these antigens in H. pylori during various culture conditions. The quantities of these antigens varied considerably (up to 8-fold) during different culture procedures and between strains (up to 10-fold).