Twenty, otherwise unselected, subjects with Type II diabetes mellitus were studied using electroneurographic and electromyographic techniques. Latencies, conduction velocities, amplitude and duration of evoked responses and change of amplitude and duration over distance, as well as H reflex and ulnar F wave were determined for motor nerves. Latency to onset and peak of negative deflection and amplitude of the evoked action potential were determined for sensory nerves. Eleven subjects had amplitude and/or latency abnormalities of the sural, superficial peroneal, and median sensory nerves. One additional subject had abnormality of both the sural and superficial peroneal nerves. Five subjects had mononeuropathies and 2 of these also had membrane instability of the abductor hallucis muscle. Ten subjects had clinical or electrophysiologic findings compatible with carpal tunnel syndrome either as an isolated lesion or superimposed on underlying peripheral neuropathy. It was concluded that all subjects with abnormality of 3 sensory nerves (median, sural and superficial peroneal) had findings compatible with diabetic peripheral neuropathy and that additional electrodiagnostic studies (unless otherwise indicated) did not identify additional abnormalities diagnostic of peripheral neuropathy in the remaining subjects.