It was just about ten years ago that platelet membrane glycoproteins were first charac terized and their abnormalities in congenital bleeding disorders first recognized. Dur ing this decade there has been a remarkable growth in our understanding of the structure and membrane organization of the platelet surface glycoproteins, their in teractions with external ligands during the process of hemostasis, and their defects causing hemorrhagic disease. These studies have advanced the knowledge of platelet involvement in hemostasis from a cellular to a molecular level, and they have provided a model...