The effect of long-term (40 min) high frequency stimulation (143 Hz) of sensory-motor tail nerves was studied in normal and in streptozotocin-diabetic rats. The study comprised a 6-week period, repeating the test at 2-week intervals. In the initial (prediabetic) study, single experiments showed a mild depression of the peak-to-peak amplitude during high frequency stimulation, which reversed completely during a subsequent rest period. In normal rats, the amplitude depression was unchanged in repeated tests over a 6-week period. Diabetic rats showed a greater amplitude depression during high frequency stimulation. The difference was statistically significant after 2 weeks, but showed no further change at subsequent tests. The greater decrease in the amplitude in diabetic rats may reflect a depression of the axon membrane function, which may be the functional correlate to the inhibition of the Na/K ATPase activity in diabetes, described by others. Monitoring of the axon membrane functional capacity may have clinical implications in the control of peripheral neuropathies.