Eighty biopsy specimens of muscles from 79 elderly patients (chiefly in the 60-90 age group) were examined by histochemical and electron microscopic methods. Neuropathic change and type-II fiber atrophy of various grades were prominent findings in the muscles from patients of advanced age. Nemaline rod formation, "ragged red" change and an increase of sarcolemmal nuclei were also common. Several electron microscopic features of the muscle fiber corresponded to those reported for various neuromuscular diseases. Various factors associated with the aging process apparently act on the motor neurons and cause the neuropathic and myopathic changes seen in the muscles of the aged.