To elucidate the contribution of glutathione S-transferase (GST) and glutathione peroxidase (GPx) to the protection against oxidative stress in rat brain, we prepared GST and GPx from newborn rat liver, brain and cultured astrocytes, and investigated the characteristics and kinetics of the enzymes. The activity of cytosolic GST of the cultured astrocytes toward 1-chloro-2,4-dinitrobenzene (CDNB) was much higher than that of GPx toward peroxides. The GST activity toward 4-hydroxy-2-nonenal (4HNE) was almost the same as the GPx activity. GST isozymes were purified from the cytosolic fraction of the liver and astrocytes. In the case of the astrocytes, a major GST isozyme with an isoelectric point (pI) of 9.02 accounted for approximately 40% of total GST activity toward CDNB, while hepatic GST isozymes showed seven peaks in the basic region. Each of astrocytes and liver showed a single GST peak with high activity toward 4HNE, namely AVIII and LVIII, respectively, and both of them had a similar pI value of about 6.7. The kinetic parameters of AVIII and LVIII were found to be similar to each other. These data suggest that the same types of GST isozymes are expressed in the astrocytes and liver, and take part mainly in the detoxification of 4HNE.