By measuring the permeability across the lipid bilayer in the presence and absence of membrane-bound protein or glycoprotein it should be possible to get an impression concerning their ability to penetrate into the membrane bilayer. Proteins such as phospholipase A2 and acetylcholinesterase markedly increase the permeability in contrast to glycoproteins (ovomucoid and orosomucoid) and cytochrome C. The results may serve as an indication of the type of interaction between lipids and membrane components.