Abstract: Objective :To assess the expression and function of P-glycoprotein (Pgp) in Gleevec-resistant leukemia cells. Methods :MTT assay was performed to evaluate the sensitivity of K562/G01cells to doxorubicin (DOX) and Gleevec.The effect of verapamil (VPL) on the sensitivity of K562/G01cells to drugs was also determined. RT-PCR and Western blotting were used to determine the expres-sion of the multidrug resistance gene mdr1 and its protein product Pgp. Flow cytometry (FCM) was usedto analyze intracellular levels of DOX and Rhodamine 123 (Rho123),as well as the modulation of Pgpfunction by Gleevec and ATP. Results :Like K562/A02 MDR cells, K562/G01 cells expressed mdr1/Pgp.However,the drug efflux function of Pgp failed to be detected in K562/G01 cells.The intracellularconcentrations of DOX and Rho123 were similar to those found in K562 cells.Adding either Gleevecor ATP to K562/G01 cells resulted in a markedly decreased level of intracellular DOX. Conclusion :Human leukemia Gleevec-resistant K562/G01 cells express dysfunctional mdr1/Pgp.The drug effluxpump activity of Pgp can be partially restored by adding Bcr/Abl inhibitor,Gleevec,or ATP.