In the present study we investigated the effect of bovine conglutinin on the phagocytic activity of leukocytes. We measured both the chemotactic activity of conglutinin and its effect on the internalization of zymosan particles and E. coli by granulocytes. We also assessed the binding of conglutinin to various microorganisms isolated from clinical cases in cattle. We showed that conglutinin binds strongly to the surface of yeast cells and to mannan-rich zymosan particles, while weak binding was observed in the case of the bacterial strains tested, including those whose O antigen is composed of mannan. Conglutinin (1-10 microg/ml) neither acts as a chemotactic factor for peripheral blood leukocytes nor affects ingestion of E. coli by granulocytes. However, as flow cytometry based assay showed, conglutinin (0.1-1 microg/ml) increased ingestion of zymosan expressed as mean fluorescence intensity (MFI) of positive cells.