The interaction of fluorescein isothiocyanate (FITC)-labelled cells of Helicobacter pylori with human polymorphonuclear leucocytes (PMNs) was studied. Two strains with surface haemagglutinins expressing different receptor specificity were used in order to decide if cell surface haemagglutinins of H. pylori may play a role in lectin-mediated binding to/uptake by phagocytes: (1) strain 17874 (NCTC 11637) which expresses sialic acid-specific haemagglutinin; and (2) strain 17875 (NCTC 11638) which expresses a sialic acid-independent haemagglutinin. Cells of strain 17874 were poorly attached to/ingested by PMNs compared to cells of strain 17875. Pre-treatment of bacteria with fetuin or rabbit antibodies against partly purified sialic acid-specific haemagglutinin enhanced interaction of cells of strain 17874 with PMNs. The enhancement did not occur in the case of strain 17875. Phagocytosis of H. pylori 17874 bacteria was slightly increased by fresh human sera positive for anti-H. pylori antibodies. The results suggest that the sialic acid-specific haemagglutinin complex of 17874 bacteria might disturb their uptake by human PMNs.