Objective To investigate the value of interphase fluorescence in situ hybridization(FISH)technique and the detection of fusion gene in the diagnosis of acute myeloid leukemia(AML)M2 and M3 Methods FISH was used to detect the AML1/ETO fusion gene and/or PML/RARα fusion gene in incipient cases including 9 AML-M2, 12 AML-M3 and 10 AML undetermined as AML-M2 or AML-M3 primarily diagnosed by routine morphology though bone marrow,cytochemical staining and immunophenotyping,which can help diagnose and guide clinical therapy.Results 4 of 9 AML-M2 cases were AML1/ETO positive.Among 12 AML-M3 cases,10 were PML/RARα positive.1 case was detected AML1/ETO fusion gene.In 10 untonfirmed M3 or M2,3 case8 showed AML1/ETO,5 showed PMIJRARot fusion gene and the rest showed neither of the genes.Conclusion As a new technique of the molecular genetics,FISH is accurate, rapid and efficient.It would be of significance not only at diagnosis of AML,but also for subsequent clinical decision-making.