This study was purposed to investigate the expression of c-fes gene in leukemia patients and its clinical significance. The expression of c-fes mRNA in bone marrow cells from 121 cases of acute and chronic leukemia patients, and the expression of c-fes mRNA in peripheral blood mononuclear cells of 20 normal persons were detected by real time-quantitative reverse transcription polymerase chain reaction (RQ-PCR). The results showed that the level of c-fes mRNA in AML patients was higher than that in normal controls [(48.017 +/- 57.170) x 10(-3) vs (0.152 +/- 0.398) x 10(-3)] (p 0.05); the level of c-fes mRNA in CML patients was higher than that in normal persons (21.605 +/- 24.818) x 10(-3) vs (0.152 +/- 0.398) x 10(-3) (p < 0.0001). The positive expression rate of c-fes gene in CML-CP patients (80%) was higher than that in CML-AP patients (66.7%) and CML-BP (28.6%) patients. In AML patients, c-fes gene was expressed higher in M(2) (80.77%) and M(3) (92.86%) patients. The remission rate of AML (except M(3))patients who had expression of c-fes gene was 81.08%, which was higher than that of patients with no expression of c-fes gene (40.00%). It is concluded that c-fes gene expression was found in myeloid leukemias, whereas low or no expression in lymphocytic leukemias. The differentiation of myelocytic cells may be related to c-fes gene. All AML (except M(3))patients with high level of c-fes mRNA may get good prognosis.