We studied the sensory and motor potentials of the median and posterior tibial nerves and sural nerves in 20 insulin-treated diabetic patients, aged 21-71 years, with a known duration of 1 month to 25 years. Individual levels of sensory velocity were within normal range or slightly reduced in diabetic patients. However, the reductions of sensory potential amplitude were obvious in the sural nerve. No relation was found between sensory amplitude and either known diabetic duration or retinal diabetic changes. These results suggest that axonal degeneration of sensory fibers cannot easily be corrected in comparison to the slight changes caused by segmental demyelination.