To investigate the effects of ethanolamine plasmalogen, phosphatidylethanolamine, cholesterol, and alpha-tocopherol on the oxidizability of membranes, various large unilamellar vesicles (LUVs) including these lipids and antioxidant were examined for their total membrane oxidizabilities, evaluated as R-p/R-i(1/2) value (where R-p is rate of oxygen consumption and R-i(1/2) is the square root of rate of chain initiation) by the oxygen uptake method with water-soluble radical initiator and inhibitor. Incorporation of bovine brain ethanolamine plasmalogen (BBEP) into vesicles as well as cholesterol led to lower the total membrane oxidizability dose-dependently. The effect of BBEP was more efficient in the presence of cholesterol in vesicles. On the other hand, diacyl counterpart, egg yolk phosphatidylethanolamine, and a typical radical scavenger, alpha-tocopherol, had no effect on the membrane oxidizability. alpha-Tocopherol only prolonged an induction period dose-dependently in the present oxidizing system, suggesting a novel antioxidant mechanism of ethanolamine plasmalogens besides the action of scavenging radicals. (C) 2003 Elsevier Science (USA). All rights reserved.