The research proposed in this application is carried out with the objective of obtaining basic information on the effect of sphingomyelin on biological membrane structure and properties and how these effects might be related to aging and atherosclerosis in blood vessels. The work outlined will utilize three systems, liposome dispersions, planar bilayers and monolayers formed at an air/water interface. Liposomes will be used to study both compositional asymmetry between opposite bilayer faces and compositional domains within the planes of the bilayer in sphingomyelin-phosphatidylcholine-cholesterol systems. Studies of bilayer permeability and structure as functions of composition and temperature will be undertaken in systems exhibiting compositional domains. Details of the interactions between these three lipids will be examined directly using monolayer techniques. In addition, permeability and transport properties, together with membrane fluidity will be studied in mammalian erythrocyte membranes obtained from a series of species exhibiting differences in the ratio of sphingomyelin to phosphatidylcholine. Similar studies on the plasma membranes of rat aortic smooth muscle cells will also be undertaken.