Nerve conduction of single impulses and the ability to transmit frequent trains of stimuli were studied in sensory median and in sural nerves of controls and patients with diabetes mellitus. Decrease of relative amplitudes and increase of relative latencies were more marked in the diabetics as compared with normal controls when trains of stimuli were applied. An altered mode of the transmission of frequent trains could be demonstrated in 7 of 9 sural nerves and in 13 of 16 median nerves, which appeared to be normal when only a single stimulus was applied.