Blood lysozyme estimation seems to be important in hematological practice. Serum levels are roughly proportional to the size of the pool and, above all, granulocytic renewal. Thus levels are increased compared with levels of circulating polynuclear cells. In bone marrow disorders, and particularly in myelofibrosis, owing to the infective granulopoiesis and/or increased destruction of the neutrophil polymorphs. It is lowered in neutropenia with a scanty bone marrow. It provides an important contribution to diagnosis of the type of acute leukemia, the fall in the lymphoblastic forms contrast with normal or increased levels in myeloblastic forms. Finally, there is a marked increase in lysosome urea in acute monocytic or myelomonocytic leukemia.