The rate of accumulation of auto-fluorescent granules (lipofuscin) in three different regions of rat brain was investigated at various ages from very young to old animals (1, 2, 3, 6, 12 and 30-34 months of age. The accumulation of lipofuscin increased with age in the three brain regions. The first appearance of lipofuscin granules was at 8 weeks of age in the hippocampus and in the thalamus. In the case of cerebral cortex (laminae III), lipofuscin granules were first found in 3-month-old rats. The rate of lipofuscin accumulation was the highest in the hippocampus (y = 0.286x - 0.099, r = 0.963) among the three regions examined. In the case of cerebral cortex and thalamus, a slower rate of lipofuscin accumulation was observed (y = 0.072x - 0.14, r = 0.797 for cerebral cortex; y = 0.067x - 0.14, r = 0.953 for thalamus). It was noted that the most abundant accumulation and the highest rate of lipofuscin accumulation was in the hippocampus. But the rate and magnitude of lipofuscin accumulation in the hippocampus were low compared with cardiac muscles. From these results, it is suggested that brains have better protective system against oxidative stress than other organs.