The major glycoprotein of the human erythrocyte membrane was isolated, purified and its overall molecular anatomy partially characterized, and labeling studies were carried out to determine how it might be oriented at the cell surface. This molecule, named glycophorin, is a single polypeptide chain which carries many blood group antigens and lectin receptors. The polypeptide chain has 3 distinct segments that have unique chemical properties and that appear to be located in different regions of the membrane. All the carbohydrates are covalently linked to the N terminal one half of the polypeptide chain and are exposed to the external environment of the cell. The C terminal one third of the polypeptide appears to be located internal to the lipid barrier of the membrane possibly extending into the cytoplasm of the cell. The segment connecting these two portions is composed of nonpolar and hydrophobic amino acids which span the lipid region of the membrane. The hydrophobic 'middle' segments of the polypeptide chains appear to be linked to 85Å globular structures located within the lipid region of the membrane. Since these globular units, first observed by freeze etching and electron microscopy, seem to be anchoring sites for the glycoprotein molecules and possibly other proteins, these complexes may be important functional units of the membrane.