Abstract - ionizing radiation increases intracellular production of reactive oxygen species (ROS), which can damage cell structure and function. The brain is particularly vulnerable to oxidative injury, and in an area-dependent manner. in order to elucidate differences in enzymatic antioxidative responses of the rat hippocampus and cortex, we measured the activities of cytosol superoxide dismutase (CuZnSOD), mitochondrial superoxide dismutase (MnSOD), and catalase (CAT) in those two brain regions, isolated 1 h and 24 h after exposure to 2 Gy of g-rays. our results indicate that the lower MnSOD activity and inducibility found in the hippocampus are probably among the main reasons for particularly great oxidative vulnerability of this brain region.