The doxorubicin-resistant, acute myelogenous leukemia cell line, AML-2/DX100, characterized by the over-expression of multidrug resistance protein (MRP) and the down-regulation of catalase, has advantages for the screening of MRP inhibitors as well as for cytotoxic substances producing potential reactive oxygen species. The screening power of AML-2/DX100 cells for an MRP inhibitor, probenecid, was approximately 4-fold stronger than that of another resistant cell line, HL-60/Adr, over-expressing MRP. AML-2/DX100 was approximately 2- to 5-fold more sensitive to pro-oxidants such as Paraquat, H2O2 and t-butyl hydroperoxide, when compared with its parental cells.