The objective of this study was to investigate the relationship between the expressions of breast cancer resistance protein (BCRP) gene and drug resistance as well as prognosis in adult patients with acute lymphocytic leukemia (ALL). Semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect the expression of BCRP gene in 97 adult patients with acute lymphocytic leukemia (ALL) and 30 normal subjects. Beta(2) microglobulin (beta(2)-MG) was used as an internal reference. BCRP/beta(2)-MG ratio >or= 0.48 was defined as BCRP positive. The results showed that the positive ratio of BCRP gene expression in untreated group was 28.7%, in contrast that in refractory and relapsed patients was 51.2%. The first complete remission rates in patients with negative and positive expression were 71.7% and 29.7% respectively. In ALL subtypes BCRP gene expression of L3 type was distinctly higher than that of L(1), L(2) types. In immune types the BCRP gene expression of B-ALL was higher than that of T cell type, especially in mature B cell type with obviously statistical significance (p<0.01). It is concluded that the high expression of BCRP gene may induce clinical drug resistance, and may be an unfavorable factor for prognosis in adult patients with acute lymphocytic leukemia.