This study was purposed to investigate the expression of B7-H1 gene in leukemia cells and its clinical significance. The expression of B7-H1 mRNA was detected by SYBR Green I real-time quantitative PCR in a panel of 9 leukemia cell lines, 4 leukemia cell lines induced with IFN-γ, the bone marrow mononuclear cells (BMMNC) from 59 initial leukemia patients and 10 dendritic cells (DC) derived from BMMNC of initial leukemia patients, 2 solid tumour cell lines and BMMNC from 10 normal persons. The correlation between the clinical features of 59 acute leukemia patients and the expression level of B7-H1 mRNA in leukemia cells was analyzed. The results showed that the lower level of B7-H1 mRNA expression was found in leukemia cell lines and primary acute leukemia cells, but the expression level of B7-H1 mRNA was up-regulated significantly in the leukemia cell lines induced by IFN-γ and DC derived from BMMNC of leukemia patients. The expression level of B7-H1 mRNA in non complete remission (CR) patients after therapy was significantly higher than that in CR patients. It is concluded that the expression level of B7-H1 mRNA in leukemia cells is lower, but is up-regulated when affected by some factors. A correlation exists between the expression level of B7-H1 gene in leukemia cells and response of patients to therapy.