Patients with multiple sclerosis commonly complain of tingling and other sensory disturbances which may occur spontaneously or in response to movement. These symptoms are associated with plaques of demyelination in the corresponding sensory pathways but the physiological abnormalities underlying the symptoms are not understood. We have examined sensory fibres traversing a central demyelinated lesion resembling that of multiple sclerosis for evidence of activity which could account for the symptoms. We present here evidence for the existence of spontaneously and mechanically induced trains of action potentials propagating in both directions from the lesion.