Since previous studies from this laboratory have suggested that glutathione S-transferase (GST) 8-8 of rat belongs to a distinct subgroup of GST isozymes which may be involved in the detoxification of the products of lipid peroxidation (Zimniak et al., J. Biol. Chem. 269, 992-1000, 1994), during the present studies we examined the effect of iron-induced lipid peroxidation on the expression of GST 8-8 in rat liver. Rats treated with 100 mg/kg body wt iron showed a significant increase in lipid peroxidation in liver. This was accompanied by a concomitant increase in the expression of GST 8-8 in liver as observed in isoelectrophoretic analysis of rat liver GSTs, and an increase in GST activity toward 4-HNE, a toxic product of lipid peroxidation toward which GST 8-8 displays high specific activity. Western blot studies using polyclonal antibodies specifically recognizing GST 8-8 also indicated that, among the GST isozymes of rat liver, GST 8-8 was preferentially induced upon iron treatment. These findings were further confirmed by purifying and quantitating GST 8-8 protein from the controls and iron-treated rats. Significant differences in the specific activities of GST 8-8 purified from the controls and iron-treated rats were observed, indicating that more than one GST isozyme related to GST 8-8 may be present in rat liver. This observation is consistent with the observed heterogeneity in mouse mGSTA4-4 which is an ortholog of rat GST 8-8. Iron treatment also caused significant increase in GSH levels probably because of de novo synthesis as indicated by an increase in gamma-glutamyl cysteine synthetase activity. The results of these studies suggest that GST 8-8, and possibly other related GST isozymes, may play an important role in defense mechanisms against lipid peroxidation.