The platelet is surrounded by a pronounced glycocalix formed by carbohydrate moieties of the membrane glycoproteins. The number of glycoproteins of the outer platelet membrane is greater in number than had previously been reported : when solubilized membranes are analyzed by SDS-polyacrylamide gel electrophoresis the number of separated carbohydrate entities was found not only to be dependant on the concentration of acrylamide and of bisacrylamide used but also on the buffer system employed.The major platelet membrane glycoproteins have been solubilized and subjected to affinity chromatography on the lectins from Lens culinaris, wheat germ and Abrus precatorius. SDS-polyacrylamide gel electrophoresis in the presence and absence of a reducing agent together with the differential binding of the lectins to the glycoproteins permitted the distinction of at least seven glycoprotein entities. Using combinations of lectin columns, two platelet membrane glycoproteins have been isolated and others have been greatly purified.