Low vitamin E levels have been found to be a frequent side effect in patients on total parenteral nutrition (TPN). In the present study, the vitamin E content of fat emulsions (Intralipid) was measured and the influence of the intravenously administered lipid emulsion on plasma vitamin E levels was investigated. The majority of vitamin E was provided in the beta + gamma-tocopherol fractions (68.7% of total tocopherol). Vitamin E levels in patients were significantly lower (p less than 0.05) as compared to age- and sex-matched normal controls. Although sufficient amounts of vitamin E (16.9 +/- 0.8 IU daily) were infused, according to RDA requirements, E-plasma levels decreased even further during the course of TPN. It was concluded that high amounts of biologically less active tocopherol isomers are not sufficient to maintain vitamin E plasma levels. Supplemental sources of alpha-tocopherol are needed and more attention should be paid to the different tocopherol isomers in the quantitation of the daily allowances of vitamin E.