A multiple analysis of the cerebral oxidative stress was performed on a physiological model of dementia accomplished by three-vessel occlusion in aged rats. The forward rate constant of creatine kinase, k for, was studied by saturation transfer 31P magnetic resonance spectroscopy in adult and aged rat brain during chronic hypoperfusion. In addition, free radicals in aging rat brain homogenates before and/or after occlusion were investigated by spin-trapping electron paramagnetic resonance spectroscopy (EPR). Finally, biochemical measurements of oxidative phosphorylation parameters in the above physiological model were performed. The significant reduction of k for in rat brain compared to controls 2 and 10 weeks after occlusion indicates a disorder in brain energy metabolism. This result is consistent with the decrease of the coefficient of oxidative phosphorylation (ADP:O), and the oxidative phosphorylation rate measured in vitro on brain mitochondria. The EPR study showed a significant increase of the ascorbyl free radical concentration in this animal model. Application of α-phenyl- N- tert-butylnitrone (PBN) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin traps revealed formation of highly reactive hydroxyl radical ( OH) trapped in DMSO as the CH 3 adduct. It was concluded that the ascorbate as a major antioxidant in brain seems to be useful in monitoring chronic cerebral hypoperfusion.