Lysozyme (E.C.3.2.17) is widespread in nature and hen egg white is a rich source of the enzyme. Membrane isolation technique of lysozyme has limited application by poor yield and purity of product. The classic enzyme precipitation and crystallisation method is still being used. The latter one is often replaced by ion exchange method that is also recommended for large scale industrial purposes as efficient and not very expensive. The application of gel filtration gives highly homogenous lysozyme with the presence of certain amount of multimeric forms of enzyme. The quantity of dimeric and other polymeric forms can be increased by thermal denaturation of the monomeric form. Irreversible lysozyme dimer formation makes the enzyme quite novel antimicrobial agent against Gram-negative bacteria. A different mechanism of the dimeric form action has been suggested. Lysozyme monomeric form is known as a natural preservative of strong antimicrobial activity, especially against the Gram-positive bacteria. Enzyme extends shelf-life of certain food products e.g. a row-chilled poultry by reducing total bacterial count as well as E.coli and enterococci. Lysozyme greatly affects Listeria monocytogenes and Clostridium botulinum but salmonellas demonstrate some resistance to enzyme action.