Three lines of evidence indicate that vitamin E is important for normal neurological function in man. First, in abetalipoproteinaemia early therapy with vitamin E delays, and may prevent, the development of neurological complications, and in patients with established lesions treatment can arrest or reverse the neuropathy. Secondly, in other chronic disorders of fat absorption with severe vitamin E deficiency, neurological manifestations can be improved by vitamin E. Thirdly, the neuropathological changes observed in vitamin-E-deficient states in man (such as abetalipoproteinaemia, chronic liver disease, and cystic fibrosis) are similar to those reported in vitamin-E-deficient rats and monkeys.