AbstractWe studied the fate of skeletal muscle obtained from patients with amyotrophic lateral sclerosis (ALS) after transplantation into immunodeficient nude mice. The transplanted muscle consistently survived in the nude mice without immunological rejection. The myofibers in these muscles underwent degeneration, followed by regeneration, maturation, and eventual functional innervation by the mouse motor neurons. The ability to grow diseased human muscle successfully over a prolonged period in nude mice offers an in vivo model to study the etiology of ALS and possibly of other neuromuscular disorders.