The clinical findings of three cases of metachromatic leukodystrophy, one of the late infantile, one of the juvenile and one of the adult variant are described and compared with those mentioned in relevant publications. Comparison of our findings lead us to conclude that a difference exists between the late infantile case on the one hand and the juvenile and the adult case on the other hand. This conclusion concurs with the results obtained by the enzymological study of the enzyme arylsulfatase A derived from the three cases. As to the characteristics of the enzyme arylsulfatase A, a difference was found to exist between the enzyme of the late infantile case on the one hand and that of the juvenile and the adult case on the other hand. The results of the electronmicroscopic investigation of peripheral nerve biopsy specimens of the three cases are briefly summarized. It is postulated that the ultrastructural findings do not justify any such distinction.