Abstract: Multidrug resistance is the main cause of chemotherapy failure,To detect multidrug resistance is helpful to develop chemotherapy regimens and more effective treatment of patients with tumors. ⁹⁹Tc^m-sestamibi is a transport sub-strate of mdr1-encoded P-glycoprotein and MRP.The lower ⁹⁹Tc^m-sestamibi accumulation indicates the higher expression of P-glycoprotein in tumor cells.It is also related to the expression of MRP.As a result,response to chemotherapy can be estimated before starting treatment by means of ⁹⁹Tc^m-sestamibi imaging and more effective protocol can be chosen.