OBJECTIVE: To investigate the expression and significance of Bcl 2 and MDR 1 genes in children with acute leukemia. Methods The expressions of Bcl 2 and MDR 1 genes in 36 cases of acute leukemia and 10 cases of idiopathic thrombocytopenic purpura in the control group were examined by RT PCR. RESULTS: The expressions of Bcl 2 in the incipient group and relapsed group were higher than that of the control group (P< 0.05 ). While in the incipient group and complete remission group, they were lower than that of the relapsed group (P< 0.01 ). The expression of MDR 1 gene in the relapsed group was higher than those of control group, incipient group and complete remission group (P< 0.01 or 0.05 ). There was no difference of MDR 1 expression between the incipient group and the control group or the complete remission group and the control group (P> 0.05 ). There was no close relationship between the levels of Bcl 2 or MDR 1 and clinical features such as gender, age, initial WBC count, the percent of carcinocytes, hepatomegaly, splenomegaly and lymphadenhypertrophy (P> 0.05 ). The relationship between Bcl 2 and MDR 1 genes was not significant (r s= 0.308 , P> 0.05 ). CONCLUSIONS: Bcl 2 and MDR 1 genes were associated with drug resistance by different mechanisms.