Severe hypoxia induces intensive DNA fragmentation in rat hippocampus. The hippocampal level of thiobarbituric acid reactive substances (TBARS) is decreased with time after severe hypoxia. Hypoxic postconditioning is protective against severe hypoxia-induced DNA fragmentation. Postconditioning normalizes the hippocampal level of TBARS and down-regulates the amount of Schiff bases.