A severe deficiency of vitamin E causes a characteristic neurological syndrome in man and experimental animals. In this study a number of electrophysiological modalities in vitamin E deficient and control rats have been investigated over a period of one year to define the time of onset and severity of the abnormalities associated with vitamin E deficiency in the rat. The mean velocities (n = 10) of the sensory evoked potentials were slower at all time points in the vitamin E deficient rats, with the central conduction velocities being more severely affected than the peripheral. Central conduction velocities, following both tibial and median nerve stimulation, were significantly delayed (P < 0.005) after 8 months of deficiency. Differences in peripheral conduction following tibial stimulation became significantly delayed (P < 0.005) after 11 months of deficiency. There were no significant differences in the brainstem auditory evoked potentials or peripheral sensory motor responses between the vitamin E deficient and control rats over the 1 year period. These results in the rat are essentially similar to those previously reported in vitamin E deficient man.