Histochemical and in particular immunoperoxidase techniques have extended our knowledge about the cellular distribution of LZM. The enzyme has been detected in: 1. granulocytes, which synthesize LZM in bone marrow; 2. cells of the mononuclear phagocytic system, which synthesize LZM continuously; 3. various exocrine glands, whose LZM is probably in part synthesized locally and in part derived from blood; 4. cartilage, which probably synthesizes LZM and 5. the kidney, in which LZM is serum-derived. In pathological conditions, such as inflammation and neoplasia, most LZM-positive cells at the site of disease are either granulocytes or members of the mono-nuclear phagocytic system. A notable exception are the metaplastic Paneth cells that occur along the gastrointestinal tract in inflammation and neoplasia. LZM is an antibacterial agent, but evidence is accumulating which suggests that the enzyme might have other functions as well.