In order to investigate the relationship between the expression of breast cancer resistance protein (BCRP) gene and drug resistance in patients with acute leukemia (AL), semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to examine the expression of BCRP mRNA in AL patients and 15 normal subjects. Beta(2)-microglobin (beta(2)-MG) was used as positive reference. BCRP/beta(2)-MG ratio >or= 0.5 was defined as BCRP mRNA positive. The results showed that the positive percentage of BCRP gene expression in newly diagnosed group was 37.6%. The first complete remission rate was 79.3% and 31.6% in BCRP mRNA negative and BCRP mRNA positive patients respectively. The difference was significant (P = 0.001). The expression levels of BCRP mRNA in drug resistance group and drug sensitive group were 0.962 +/- 0.426 and 0.315 +/- 0.296 respectively (P = 0.0001). The expression level of BCRP mRNA in relapsed/refractory group was significantly higher than that in newly diagnosed group (P = 0.0025). The expression level of BCRP gene in normal individuals and long-term survival group was very low and correlated with FAB subtypes. It is concluded that high expression of BCRP mRNA leads to clinical drug resistance and is an unfavorable factor for prognosis of AL patients except acute promyelocytic leukemia.