). The implication of such a model is that all plasma membrane proteins are considered to be uniformly dispersed in the lipid solvent, akin to “icebergs in a sea of lipid.” Many independent investigators in the past decade, however, have provided evidence for the existence of other lipid bilayer states, namely “liquid-ordered” membranes. These regions are enriched in cholesterol and sphingolipids (Table 1), making them more ordered and less fluid than the bulk plasma membrane. As a consequence, these membranes are resistant to solubilization with nonionic detergents at low temperatures (