High MDR1 gene expression is a common feature of AML resistance to conventional chemotherapeutic regimen.18,19 One of the strategies that overcome MDR is to increase the pharmacal liposolubility and elevate the intracellular drug concentration, so as to counteract drug efflux pumped by P-glycoprotein. Idarubicin (IDA), a new anthracycline, has more strengthened liposolubility and can easily permeate the cell membrane in comparison with traditional marcellomycin. Also, the in vivo metabolite of IDA (4-IDA) has the same antineoplastic activity as IDA and a longer half-life in vivo. It can also permeate blood brain barrier. As a result, IDA has a stronger antileukemia activity than other marcellomycin and can partially overcome P-glycoprotein-mediated drug resistance.20, 21 In our recently pilot study, we have detected the expression of MDR1 in pre-treated bone marrow samples from 160 de novo AML patients and the median value of MDR1/GAPDH ratio in the de novo AML cases was 0.016（0-81.865）. The median value of MDR1 gene expression was taken as the cut-off point of high or low MDR1 gene expression levels. For high MDR1 expression patients, a lower CR rate (61.3%) was observed compared with low-MDR1 expression patients (80.0%, P =0.009). In this retrospective pilot study, 123 patients were received daunorubicin (DNR 35~45mg/m2/d,3 days) or idarubicin (IDA 6~8 mg/m2/d, 3 days) in combination with cytarabine (Ara-c100~200 mg/m2/d, 7 days) for remission induction and significant difference were also observed after 2 courses of chemotherapy between those who receive IA regimen (57 cases) and DA regimen (66 cases) regarding to CR rate (80.7% vs 57.6%, P=0.006). Significant difference could also be discovered between two treatment arm with regard to CR rate (75.9% vs 43.6%, P=0.011) in those who had high MDR1 expression AML patients. Our data shows that IDA may overcome MDR1 induced chemoresistance with a higher CR rate than DNR in de novo high MDR1 expresser AML patients.These results provide rationale for development of randomized, prospective trial to compare the CR rate of IA regimen and DA regimen in de novo AML patients with high MDR1 expression and to identify whether Idarubicin can overcomes MDR1 induced chemoresistance with higher induction remission rate than daunorubicin in de novo acute myeloid leukemia patients. We speculated that the more favorable outcome in high-MDR1 patient group with IA regimen may be associated with a higher remission rate.