Plasma triglyceride-rich lipoproteins vary in lipid composition during their metabolism: specifically their cholesterol and its ester content. It has been believed that the alteration in the physical state of surface membranes caused by these lipids is the major determinant in the binding of exchangeable apoliopoproteins. Recent studies using lipid emulsions of defined composition have shown that the interaction between surface and core lipids modulates the emulsion surface structure and the apolipoprotein binding. The increase in surface cholesterol in emulsions increased the surface rigidity and decreased the binding capacity of apolipoprotein. In addition, cholesteryl oleate was shown to significantly decrease apolipoprotein bindings through the unique mechanism by which it not only decreases the core mobility but also causes the relocation of cholesterol in the emulsion surface layers. These results provide a new insight into the mechanism how the increases in surface cholesterol and core cholesteryl ester exert their effects on the lipoprotein metabolism.