In this paper the in vitro effects of lysozyme on several immunological function was investigated. Henn-egg-white lysozyme (at concentrations ranging between 1 and 10 micrograms/ml) has shown an inhibitory action on mitogen-induced lymphoblastigenesis and autologus mixed lymphocyte reaction. On the other hand, NK activity against K 562 cell line resulted to be increased in the presence of lysozyme. In addition lysozyme has shown to behave as chemokinetic factor increasing PMN random locomotion and inhibiting PMN response only towards complement derived chemotaxins, whereas there was no effect against other chemotactic factors. Then, in addition to its enzymatic activity, a role of lysozyme as modulator of the inflammatory response may be proposed.