In the first section the assay methods of lysozyme are reviewed. It is pointed out that there is no method using the hydrolysis of NAM- > beta-1, 4-glycoside bond- > NAG, So to clarify relation between methods will lead to discovery of new isozymes. In the second chapter serum or urinary lysozyme levels are discussed in the states of diseases. The high levels are induced by cell proliferation which are producing lysozyme. The type of cells and their nature may infer different lysozymes that has no clear evidences yet. In the third part lysozyme is reviewed as protein and product of gene. In the final, enzyme kinetics are the subject of investigation, and further studies may by chance conduct us to find out new isozymes of lysozyme in near future.