MODERN interest in amyotrophic lateral sclerosis stems from the pioneer publications of Duchenne1 and Aran,2 in which progressive spinal muscular atrophy was described and its muscular origin postulated. Opinion regarding the pathogenesis was divided thereafter between those who considered muscle and those who considered spinal cord the site of origin of the disorder. It remained for Charcot and Joffroy3 to describe amyotrophic lateral sclerosis for the first time, and their classic papers gave overwhelming support to the neurogenic concept. In 1875 Erb4 wrote about "a little-known spinal symptom complex," which since has been called primary lateral sclerosis. These conditions form the group known as "motor neuron disease," which also includes some special types characterized by aberrant age of onset (the progressive muscular atrophy of Werdnig and Hoffmann) or involvement of specific nuclei, such as Duchenne's progressive bulbar palsy. Motor neuron disease, therefore, may be manifested by