The usefulness of performing late response studies for the detection of peripheral nerve dysfunction has been demonstrated. It has been shown that significant prolongation of the minimal latencies of the H reflex and the F response is present at a time when conventional methods of motor and sensory conduction do not show an abnormality in individual patients. Abnormalities of late responses have been shown to occur in a variety of peripheral neuropathies with "axonal" as well as "segmental demyelination" type of underlying pathology.