The study was aimed at evaluation of properties of serine protease produced by Staphylococcus aureus V8. Influence of enzyme on chemotactic and phagocytic activity of rat lung macrophages was investigated. Chemotactic activity of rat lung macrophages was studied by application of modified Boyden chambers. Slight induction of chemotaxis of cells preincubated with enzyme was found. Phagocytic activity of rat lung macrophages was investigated by application of Varian E3 spectrometer. EPR signals emitted by paramagnetic graphite phagocytized by macrophages were measured. Increased phagocytic activity of macrophages subjected to preincubation with enzyme in concentration of 10 micrograms/ml was observed. It seems that staphylococcal proteinase is engaged in interaction of staphylococci with immunological system cells.