Electrophysiological examination has been used to evaluate diabetic polyneuropathy. However, most researchers evaluate the conduction velocity; few of them deal with the compound muscle action potential or sensory nerve action potential. We studied the efficacy of measuring the amplitude in 40 non-insulin dependent diabetes mellitus patients. We measured the conduction velocity and amplitude of ... [Show full abstract] the posterior tibial and sural nerves. There was a significant correlation between the conduction velocity and amplitude in the tibial nerve, but not in the sural nerve. The frequency of abnormalities was significantly higher in conduction velocity of the tibial nerve and amplitude of the sural nerve. These results suggest that measurement of the conduction velocity of the tibial nerve or the amplitude of the sural nerve is useful for evaluating diabetic polyneuropathy.