SummaryContent of calcium, manganese and aluminum in CNS tissue was measured by neutron activation analysis in four ALS and three control cases with the following results:(1) The increase in calcium and aluminum contents in CNS tissue of ALS cases were found with localization of these metals in the degenerated areas of ALS while manganese content showed no significant difference between ALS and controls.(2) Two of the four ALS cases showed a positive correlation between calcium and manganese and the other two ALS cases between calcium and aluminum, while all three control cases showed no correlation between these metals.(3) These findings suggest that the degenerative changes in ALS may be due to soft tissue calcification with interaction of other metals such as aluminum, manganese, and so on.(4) The importance of the possibility of aluminum participation in a calcifying process producing degeneration was emphasized in terms of the etiology of ALS.