Phospholipids are the primary constituents of biological membranes. Recently, phospholipids have been directly implicated in the important biological functions as well as biomembrane structure. Sphingomyelin in particular was found to be vital for formation and maintenance of lipid rafts, where immune responses, various kinds of signaling, and certain material transport take place. Sphingomyelin is thus involved in expression of specific cellular functions, such as intracellular information transmission and maintenance of membrane structure. Sphingomyelin, with long fatty acid chains and low phase transition temperatures (Tc), is easy to prepare into liposomes. Highly pure sphingomyelin of either the milk or yolk origin is available from NOF. Sphingomyelin from yolk has fatty acid chains consisting of about 80% palmitic acid joined by amide bonds, while that from milk contains many kinds of fatty acids whose chains are longer than palmitic acid. These two sphingomyelin products slightly differ in physical properties, and can be selected according to needs.