The human erythrocyte membraneskeleton protein 4.1 interacts with glycophorin C/D (GPC/D ). This interaction particularly determines the shape and the mechanical properties of the red cell. A number of workers have provided evidence for the interaction. Recent publication has reported that GPC/D provide major membrane binding sites for protein 4.1 in normal erythrocyte, and the sites are located on amino acid residues 82～98 of GPC and 61～77 of GPD.