A similar diagrammatic approach shows how demyelination affecting nerves of different diameters will produce various combinations of potentials that are delayed, small or polyphasic. In extreme pathology conduction will be blocked. Clinical examples relating to sensory and motor studies are included. By contrast with the findings in degeneration, the location of demyelination may often be easily achieved by the demonstration of abnormal conduction over the segment between the stimulating and recording electrodes. This is also explained diagrammatically and clinical examples are included. The value of limiting the distance between stimulating and recording electrodes when trying to localise a mild lesion is illustrated by examples of palm to wrist studies in carpal tunnel syndrome.