In the present paper on plasmalogens, their tissue distribution, analyzing methods, functions, deficiency, biosynthesis and its regulation, and plasmalogen in blood are summarized. In the section of analyzing methods, HPLC method using radioactive iodine, which was recently developed by author for the routine measurement of plasmalogen concentration in blood plasma, is described. In the section of functions, a novel antioxidant action of ethanolamine plasmalogen in lowering the oxidizability of cholesterol in phospholipid bilayers as well as whole membranes, which was found by author at the first time, is described. In the section of plasmalogen in blood, our data confirmed significant reduction of plasmalogen concentration in blood plasma by aging and hyperlipidemia. And our recent study on blood lipoprotein profiles from 148 elder subjects including hyperlipidemia revealed that the molar ratio of choline plasmalogen to ethanolamine plasmalogen (CP/EP ratio) in blood plasma significantly correlates with the size of low-density lipoprotein (LDL), which suggests that plasmalogens are involved in the appearance of small, dense LDL. The meaning of CP/EP ratio, and the validity of improving the value on normalizing LDL size by ingestion of sesame or plasmalogen itself are discussed.

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