The effects of dietary tea catechins on the levels of alpha-tocopherol and lipid peroxidation in both plasma and erythrocytes, as well as their effects on erythrocyte deformability, were examined in rats fed on high palm and perilla oil diets. The decrease in alpha-tocopherol concentration and the increase in lipid peroxidation level were much more pronounced in the perilla oil group than in the palm oil group. The addition of tea catechins to these diets significantly prevented the alpha-tocopherol concentration from decreasing. These results suggest that tea catechins may counteract a decrease in alpha-tocopherol by acting as an antioxidant in vivo. Furthermore, the lipid peroxidation in the plasma of rats fed perilla oil was slightly but significantly reduced by the supplemented tea catechins. However, no measurable differences were observed in the deformability of the erythrocytes in any of the groups. It is therefore likely that the erythrocytes are not severely enough affected by the lipid peroxidation to influence their deformability.