In this study we used cerebral ischaemia-reperfusion injury (IRI) as an experimental model to analyse the effects of Bio-normalizer (BN, a naturally fermented health food product) on reactive oxygen species related changes in different brain regions of gerbils. Pre-administration of BN solutions (0.1% and 1%) for 45 days produced a significant reduction in IRI-mediated increase in membrane lipid peroxidation, as shown by the decreased carbon-centred radicals and thiobarbituric acid-reactive substances in several brain regions including the cerebral cortex, the hippocampus and the striatum. BN however has no effect on the mitochondrial superoxide dismutase activity.