We analyzed changes in activity of SDH, one of the most important enzymes of the Krebs cycle, in the cytoplasm of hippocampal and cortical neurons of Mongolian gerbils (Meriones unguiculatus) at the early and delayed reperfusion period after global brain ischemia. The data indicate that SDH activity in pyramidal neurons of various hippocampal areas and in neurons of II, III and V layers of cerebral cortex after 7-min forebrain ischemia depends on both the localization of these neurons and duration of the postischemic reperfusion. SDH activity in neurons significantly increased on days 2 and 7 after reperfusion.