A Quick Staining Method for Myeloperoxidase

A staining method using 3-amino-9-ethylcarbozole for staining blood and bone marrow granulocytes for myeloperoxidase (MPX) is described. Former methods for staining for MPX with benzidine compounds have had to be discarded, as (with few exceptions) benzidine is no longer desirable nor available because of its carcinogenic properties. The staining method described herein depends on the principle that peroxidase catalizes the oxidation of 3-amino-9-ethylcarbozole by hydrogen peroxide, giving an insoluble red product.1 The method is rapid, requiring only 30 s for fixation, 2 1/2 minutes for incubation, and 5 minutes for counterstaining with hematoxylin.