Investigations that have influenced the promotion of vitamin E supplementation are reviewed. The various forms of vitamin E found in foods and the composition of synthetic vitamin E in common use are described with note of a frequent error of identification made in reports of studies on vitamin E. Recent communications on the use of antioxidants to delay carcinogenesis in animals and in humans are discussed. The publicity given the reports of cancer prevention by antioxidants will probably increase self-supplementations. It is therefore necessary to understand the pharmacological limits of such supplementation with vitamin E. Daily supplementation of adults with about 200 mg of d-alpha-tocopherol equivalents per day has not been proven to be harmful, but the effects of ingestion of more than 800 mg a day have not been studied sufficiently. Special precautions should be taken in administering emulsified vitamin E preparations intravenously to premature infants.