Leukocidins are novel leukolytic bicomponent toxins composed of S and F class protein subunits. They are one of major virulence factors produced by various strains of Staphylococcus aureus. Leukocidin subunits bind to phagocytes sequentionally (S prior to F) forming transmembrane pores. The purpose of our study was to determine the in vitro influence of staphylococcal leukocidin LukE/LukD on respiratory burst activity (RBA) of phagocytic cells (neutrophils and macrophages) isolated from head kidney of common carp (Cyprinus carpio L.). The results showed that the highest concentrations of the complete leukocidin LukE/LukD and its LukE subunit (5000-25000 µg/ml) significantly reduced RBA of head kidney phagocytes. Slight stimulation of RBA was observed at the lowest concentrations of the complete leukocidin LukE/LukD used in the experiment (0.32-1.6 µg/ml).