A prospective study was carried out on 24 volunteers who had suffered from paralytic poliomyelitis up to 51 years earlier. A quantitative EMG was carried out in each subject. Grossly raised mean amplitudes of the interference patterns were found in many strong muscles as well as in weak muscles. Such muscles frequently showed "contraction fasciculation", a manifestation of loss of normal small motor units. In many subjects the clinical and EMG evidence of chronic partial denervation were more widespread than the subjects had realised. It is suggested that if, with advancing age, minor damage occurs to the peripheral nervous system and the complement of motor neurones is already depleted by poliomyelitis, there will be an exaggerated response with increase in the lower motor neurone signs.