Feeding mice with 2(3)-t-butyl-4-hydroxyanisole (BHA) induces phase II detoxifying enzymes that inhibit the action of carcinogens. We have found that dietary BHA induces intestinal and hepatic MSP23 (also called peroxiredoxin I), a stress-inducible antioxidant, in a manner similar to the induction of glutathione S-transferases (GSTs). The levels of MSP23 in the proximal intestine and liver, estimated by immunoblotting, increased approximately 1.9- and 1.3-fold, respectively, in mice fed a diet containing 0.7% (w/w) BHA for 7 days. The level of MSP23 mRNA in these tissues also increased more than 2-fold after mice were fed BHA, suggesting that the induction of MSP23 is controlled at the transcription level. Immunostaining of the small intestine shows that MSP23 is expressed mainly in the columnar epithelial cells. The induction of MSP23 may be important to protect the cells and tissues against toxic electrophiles and reactive oxygen species.