Abnormalities of the motor and sensory innervation of muscle spindles were found in a child with a polyneuropathy of the Dejerine-Sottas type. Sensory abnormalities consisted of an increased number of IA sensory nerves and elongated primary endings in four of 10 spindles studied. The number of gamma axons was decreased. Some gamma axons were of large diameter and possessed several dozen sphere-shaped endings. Less profound abnormalities of motor endings on extrafusal muscle were observed. In a previous study of this patient it was impossible to demonstrate myelin in peripheral nerves using histologic techniques. By electron microscopy minimal amounts of myelin were found on a few axons. The nerves in spindles, therefore, were presumed also to be unmyelinated. These abnormalities again confirm the involvement of muscle spindles in disorders of the peripheral nervous system. Their contribution to the clinical symptoms is yet unknown.