Lysozyme is a 14 kd enzyme directed against the b 1 a 4 glycosidic bond between N-acetylglucosamine and N-acetylmuramic acid residues that make up peptidoglycan. Lysozyme is an antimicrobial protein secreted by polymorphonuclear leukocytes and is widely distributed in secretions such as airway secretions and nasal fluid whereas it is the most effective antimicrobial protein. It is also produced by monocytes, macrophages and epithelial cells. Lysozyme is able to kill bacteria by enzymatic lysis of bacterial cell walls and by a nonenzymatic mechanism. Allthough lysozyme is highly active against many gram-positive bacteria it is ineffective against gram-negative bacteria unless potentiated by certain cofactors (lactoferrin, antibody-complement or hydrogen peroxide-ascorbic acid). Next to its antimicrobial activity lysozyme has many other physiological functions including inactivation of certain viruses, important roles in surveillance of membranes of mammalian cells, immune regulatory activity, anti-inflammatory and antitumor activity