Objective: To explore the roles of intracellular pH value (pHi) and sodium-hydrogen exchanger isoform-1 (NHE-1) in the mechanism of multidrug resistance of leukemia cells. Methods: Multidrug resistant cell line HL-60 induced by doxorubicin(DOX) (called as HL-60/DOX cells) and their parent cell line HL-60 were employed as experiment group and control group. The proliferation and chemosensitivity of the cells were studied by MTT assay, and the expression of multidrug resistance protein (MRP) was detected by immol/Lunocytochemistry. Meanwhile, pHi was measured by spectrofluorometery with a fluorescence dye BCECF-AM. Based on the pHi recovery curve after intracellular acid loading, the activity of NHE-1 was analyzed. The expression of NHE-1 mRNA and MRP mRNA were determined by semi-quantitative RT-PCR. Cell apoptosis was observed with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), and apoptotic DNA was extracted and electrophoresed. Results: ① The IC 50 values for DOX, MTZ, VCR and homoharringtonine(HT), in HL-60/DOX cells were significantly higher than those in HL-60 cells (P<0.01). HL-60/DOX cells expressed abundant MRP, but HL-60 cells did not. ② pHi of HL-60/DOX cells were significantly higher than that of HL-60 cells(P<0.001). The expression and activity of NHE-1 in HL-60/DOX cells were significantly stronger than those of HL-60 cells. ③After administration of the specific NHE-1 inhibitor dimethyl amiloride (DMA) at a certain range of concentrations, compared with HL-60 cells, the rate of growth inhibition of HL-60/DOX cells increased significantly (P<0.05), the drug-sensitivity of HL-60/DOX cells was significantly sensitive (P<0.01), the expression of MRP and MRP mRNA decreased significantly (P<0.01), the apoptosis rate increased significantly (P<0.01). Conclusion: NHE-1 is involved in the drug-resistant mechanisms of multidrug-resistant HL-60 cells induced by DOX. The specific NHE-1 inhibitor DMA can partly reverse the multidrug resistance of HL-60 cells induced by DOX. Methods: Multidrug resistant cell line HL-60 induced by doxorubicin (DOX The proliferation and chemosensitivity of the cells were studied by MTT assay, and the expression of multidrug resistance protein (MRP) (referred to as HL-60 / DOX cells) and their parent cell line HL-60 were employed as experiment group and control group. ) was detected by immol / Lunocytochemistry. Meanwhile, pHi was measured by spectrofluorometery with a fluorescence dye BCECF-AM. Based on the pHi recovery curve after intracellular acid loading, the activity of NHE-1 was analyzed. and MRP mRNA were determined by semi-quantitative RT-PCR. Cell apoptosis was observed with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), and apoptotic DNA was extracted and electrophoresed. Values ​​for DOX, MTZ, VCR and homoharringtonine (HT), in HL-60 / DOX cells were significantly higher than those in HL-60 cells The expression and activity of NHE-1 in HL-60 / DOX cells were significantly stronger than those of HL-60 cells (P <0.001) HL-60 cells. ③ After administration of the specific NHE-1 inhibitor dimethyl amiloride (DMA) at a certain range of concentrations, compared with HL-60 cells, the rate of growth inhibition of HL-60 / DOX cells increased significantly The drug-sensitivity of HL-60 / DOX cells was significantly sensitive (P <0.01), the expression of MRP and MRP mRNAs significantly decreased (P <0.01) : NHE-1 is involved in the drug-resistant mechanisms of multidrug-resistant HL-60 cells induced by DOX. The specific NHE-1 inhibitor DMA can partly reverse the m ultidrug resistance of HL-60 cells induced by DOX.