1. Platelets have been isolated from plasma and their surface glycoconjugates radioactively-labelled using galactose oxidase and NaB3H4. 2. Conditions have been defined for optimal labelling of glycoproteins and a membrane fraction enriched in plasma membrane has been prepared and characterized by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 3. Desialylated glycoproteins that act as receptors to peanut agglutinin and lentil lectin have been purified from a detergent extract of plasma membrane. 4. Two glycosylated polypeptides that are able to bind to the surfaces of platelets have been identified and some characteristics of the binding have been investigated.