Two patients with acute myeloblastic leukemia with t(6;9)(p23;q34) translocation and classified as AML-M2 relapsed as acute monocytic leukemia (AML-M5). Trisomy 8 was found associated with t(6;9) at that time in both patients. Such changes in differentiation of leukemic cells have not previously been reported in this subtype of AML and add data favoring the pluripotent nature of the stem cell involved in leukemia with t(6;9).