Auer rods in mature granulocytes and monocytes.

In a 73-year-old man with acute myelomonocytic leukemia (M4 on FAB classification) Auer rods were demonstrated in mature granulocytes and monocytes in the blood as well as the bone marrow. Cytochemically, a significant number of leukemic blasts were positive for both alpha-naphthyl-acetate esterase and naphthol-AS-D-chloroacetate esterase. Auer rods in mature granulocytes were associated with immature cytoplasm and not infrequently with pseudo-Pelger anomaly. The significance of these observations is discussed.