A 42-year-old man was diagnosed as having acute myelocytic leukemia in July 1998. The leukemic cells tended to be differentiated, and on the basis of positive peroxidase staining, this case was considered to be AML (M2) according to the FAB classification. t(8;21)(q22;q22) chromosomal abnormality was observed, but surface antigen analysis revealed no expression of either CD13 or CD33, a finding characteristic of myelocytic leukemia. Combination chemotherapy resulted in complete remission, and allogeneic bone marrow transplantation was performed with donor cells from the patient's sister. Unfortunately, however, the patient died about 18 months after the onset of leukemia. Comparison of the findings at recurrence with those at initial diagnosis revealed morphological changes in non-differentiated immature cells (AML-M1) and CD13 surface antigen expression. This was considered to be a rare case of AML with neither CD13 nor CD33 expression at onset, but with CD13 expression at recurrence.