Vitamin E activity of sesame seed, which contains only gamma-tocopherol, a compound that has vitamin E activity equal to only 6-16% that of alpha-tocopherol, was examined in two experiments. In the first experiment, groups of rats were fed four diets: vitamin E-free control diet, alpha-tocopherol-containing diet, gamma-tocopherol-containing diet and sesame seed-containing diet. Changes in red blood cell hemolysis, plasma pyruvate kinase activity, and peroxides in plasma and liver, as indices of vitamin E activity, were examined. The sesame seed diet has high vitamin E activity, whereas this activity was low in the gamma-tocopherol diet. In plasma and liver, alpha-tocopherol was found in high concentration only in the alpha-tocopherol-fed group, and gamma-tocopherol was found in high concentration only in the sesame seed-fed group, with negligible amounts of gamma-tocopherol in liver of the gamma-tocopherol-fed group. In the second experiment, two diets containing sesame lignan (sesaminol or sesamin) and gamma-tocopherol were tested. Results in both of the sesame lignan-fed groups were comparable to those observed in the sesame seed-fed group in Experiment 1. These experiments indicate that gamma-tocopherol in sesame seed exerts vitamin E activity equal to that of alpha-tocopherol through a synergistic interaction with sesame seed lignans.