AN UNUSUAL, histochemical abnormality was found in the muscle biopsy of a patient with severe congenital weakness. The pattern of widespread hypotrophy and central nuclei affecting virtually all of the type I muscle fibers and a minority of the type II fibers was accompanied by normal histology of the brain, spinal cord, and peripheral nerves. The difficulty in determining whether this muscle abnormality indicates a major disease of muscle fibers only (a myopathy) or whether it reflects defective motor innervation and, thereby, represents a form of neuropathy will be considered. Report of a Case The patient (NIH—061967) was the second child of a healthy, 22-year-old mother. Fetal movements were thought diminished, but the pregnancy was otherwise uneventful, and the mother took no medication. Labor was induced at term. The delivery progressed normally, but the child was born apneic. After three minutes of resuscitation, respirations were present, but he remained