The purpose of this study was to investigate the adaptive mechanisms of hydrogen peroxide-supersensitive AML cells against the reactive oxygen species (ROS). Their scavenging capacity against ROS was determined using a fluorometric probe in the doxorubicin-resistant AML-2/DX100 cell characterized by the down-regulation of catalase. AML-2/DX100 cells had more scavenging capacity against endogenous pro-oxidants than did the parental cells AML-2/WT, suggesting that an anti-oxidant adaptation against ROS occurred. cDNA microarrays for 8000 human genes revealed that among 21 anti-oxidant genes, each four gene was up- and down-regulated more than 1.5-fold in AML-2/DX100 compared with AML-2/WT. The mRNA expression of glutathione S-transferase Pi, peroxiredoxin 2, thioredoxin 2, and glutaredoxin was elevated whereas that of peroxiredoxin 3, metallothionein-1F, superoxide dismutase 2, and thioredoxin reductase 1 was depressed. The result indicates that the down-regulation of certain anti-oxidant mechanisms can be compensated for by the up- and down-regulation of the other anti-oxidant mechanisms.