Ultrastructural studies of peripheral nerves and motor end-plates are performed in a case of neuroaxonal dystrophy already diagnosed on the basis of clinical and morphological data (brain biopsy). Lesions similar to those described in the central nervous system are found in the extra- and intrafusal axons and motor end plates. The sensory nerve shows only discrete alterations. Although it is widely recognized that many other diseases are characterized by the presence of axonal spheroids, the combination of the relevant clinical data and the positive results of a motor end-plate biopsy allow the diagnosis of infantile neuroaxonal dystrophy to be made, obviating or alleviating the need of a brain biopsy.