The interaction between alpha-tocopherol and ascorbate in protecting membrane lipids from peroxidation was studied in unilamellar liposomes in which alpha-tocopherol was incorporated into the liposomal membrane, and ascorbate was trapped within the vesicles. Extravesicular ferricyanide was reduced by ascorbate-derived electrons, and this was enhanced by the presence of alpha-tocopherol in the lipid bilayer. When a water-soluble free radical initiator was added to the outside of liposomes, intravesicular ascorbate prevented oxidation of alpha-tocopherol, and this effect was associated with complete protection against peroxidation of membrane lipids. These results suggest that ascorbate-dependent recycling of alpha-tocopherol can protect biological membranes from peroxidation by oxidants originating across the membrane bilayer from ascorbate.