Using the average technique of the electronic computer, we recorded the somatosensory evoked Potentials (SEPs) by electrical stimulation of median nerve (MN) and posterior tibial nerve (PTN) in twenty-three normal subjects and twenty-five diabetic patients. The peak latencies of SEPs components were prolonged, and the afferent conduction velocities of MN and PTN were reduced in most patients. In some patients, the central conduction time (N13-N20 and P40-N80 conduction time) was prolonged. Besides, there was a significant change in the shape of triphasal potentials recorded from Erb's point.and popliteal fossa. These results suggest: there not only was abnormality of conductive function of peripheralnerves, but also, the conductive function of central nervous system might be involved in diabetes mellitus.