AML-1/ETO fusion gene is the frequent genetic lesion described in FBA M(2) type acute myeloid leukemia (AML-M(2)) and is associated with a favourable prognosis. In spite of its potential clinical relevance, this subtype leukemia usually would be undetected with conventional cytology procedures, and easily confused with acute promyelocyte leukemia (APL) in morphology. In order to investigate the immunophenotypic characteristics of bone marrow cells in AML-M(2) patients with AML-ETO gene rearrangement classified by FAB, immunophenotype of bone marrow cells in 17 AML-M(2) patients with AML-1/ETO(+) confirmed by fluorescence in situ hybridization was analyzed by using flow cytometry as compared with immunophenotype in 34 APL patients with AML-1/ETO(-). The results showed that population of blast cells (15.89% - 68.53%) and population of more heterogeneous myeloid cells were detected with right-angle scatter in 17 patients with AML-1/ETO(+), i.e. AML-M(2) by FAB classification. The blast cells expressed stem cell associated antigens CD34, HLA-DR and myeloid antigens CD33, CD13, MPO. The mean fluorescent intensity of CD33 in M(2)/ETO(+) patients was significantly lower than that in APL patients (121 +/- 92 vs 845 +/- 523, P<0.001), meanwhile positive expression rates of HLA-DR, CD19 and CD34(+)CD56(+) in M(2)/ETO(+) patients were significantly higher than that in APL patients (100%, 88.24%, 100% vs 27.27%, 8.82%, 0%, P<0.001), expression rate of CD9 in M(2)/ETO(+) patients was significantly lower than that in APL patients (P<0.001). In patients with M(2)/ETO(+) (AML-M(2)), the pattern of CD15/CD11b expression was seen as granulocytic differentiation with immature events showing CD15(+)CD11b(-) and more mature CD15(+)CD11b(+) populations, the expression of mature granulocytes CD10 was negative and similar to APL in expression figure. The granulocytes expressed CD56 in 17 patients with M(2)/ETO(+) (17/17, 100%) and its expression rate was significantly higher than that in patients with M(3) (6/34, 17.56%). It is concluded that AML-M(2) with AML-1/ETO gene rearrangement was confirmed to express an exclusive immunophenotype that shows highly predictive value for the cytogenetic pattern, and the multiparametric flow cytometry with FISH provides a technical approach to easily distinguish leukemia subtype M(2)/ETO(+) from APL.