Cathepsin G expression in normal tissues is restricted to granulocytes, especially neutrophils. However, mononuclear phagocytes have been demonstrated to bind and internalize proteases from neutrophils. Cathepsin G is located in neutrophilic polymorphonuclear leukocytes which contain specialized azurophil granules together with two other serine proteases; elastase and hepsin. These three proteases may participate in the killing and digestion of engulfed pathogens and in connective tissue remodeling at sites of inflammation. Cathepsin G is also reported to be expressed in acute and chronic myeloid leukemias whereas acute lymphoblastic or chronic lymphocytic leukemias are negative for this protein.