A considerable amount of information has now accumulated which relates to the structure and behaviour of components of the eucaryote outer surface. It is thus possible to begin to derive a fairly detailed picture of this region of the cell membrane. This is particularly true for the carbohydrate chains of glycolipids and glycoproteins, about which there is good agreement. Such chains occupy totally hydrophilic environments. They possess considerable mobility relative to the macrostructures to which they are attached, yet they are constrained by rather severe potential energy barriers to oscillate about preferred conformations. Various polypeptides make up the other major outer surface feature. A point made here is that there is good reason to expect the membrane surface to be densely covered by protein, of which a substantial component will be material adsorbed from the surrounding environment. These features are illustrated in a scale drawing which emphasizes the potential for receptor modulation by interactions within the glycocalyx.