The age dependent loss of nerve cells was investigated in 22 brain areas from young (3 month), adult (13 month) and old (25 month) Sprague-Dawley rats. As in previous studies, we observed an age-related neuronal loss primarily in the archicortex and in the hippocampus and in other subcortical structures (amigdaloid nucleus, pontine nuclei, cerebellar cortex). In sensory areas of cerebral cortex the neuronal loss was less marked. The effect of a 6 month treatment with acetyl-L-carnitine (ALCAR) on the number of nerve cells in the same brain areas was also investigated. ALCAR treatment began when the rats were aged 16 months. ALCAR treatment was able to counteract the age-dependent decrease in nerve cell number primarily in the temporal and occipital cortical areas, in the archicortex and hippocampus. The above findings suggest that long term ALCAR treatment may be effective in slowing down the age-related nerve cell loss in some rat brain areas.