The correlation between kinetic metal behaviour and the degenerative process in the central nervous system (CNS) tissues of magnesium (Mg) deprived animals was examined, with particular reference to the levels and ratios of Mg, calcium (Ca), and aluminium (Al). Al content in the CNS tissue was high in the groups fed low Mg and low Mg + low Ca diets, as well as those supplemented with Al. In the group given a normal Mg, normal Ca with high Al diet, Al content in the CNS tissue showed no difference compared with that of the control group, although the concentration of Al in the serum was high. It was observed that Al content tended to rise with an increase in the Mg/Ca ratio in the CNS tissue. There was neither atrophy nor degeneration of the anterior horn cells of the spinal cord, nor demyelination of the pyramidal tract, which are characteristic of the pathology of amyotrophic lateral sclerosis. The cell body, nucleus, and nucleolus of the spinal neurones, however, appeared to diminish in size in the groups fed a low Mg diet and low Mg, low Ca with surplus Al diet. On the basis of these findings, it is speculated that Mg depletion, by increasing the Ca/Mg ratio in the CNS tissues, accelerates the uptake of Al into the brain, and this may later be involved in the development of the degenerative process.