The cause of the abnormal resistance to ischaemia of peripheral nerve function in diabetes is unknown. Median nerve function was more resistant to ischaemia in diabetic patients than in control subjects. In diabetic patients the degree of resistance to ischaemia correlated closely with HbAlc but not with the coincident blood glucose level, the duration of diabetes, the vibration perception threshold at the thumb or the initial median nerve action potential amplitude. Thus in diabetes the resistance of peripheral nerve function to ischaemia is dependent on medium term metabolic control and is not directly related to the presence or absence of neuropathy.