THE presence of fibrinogen, γM-globulin, γG-globulin, albumin and plasminogen on or in normal washed platelets has been demonstrated by the use of specific antisera^{1â 4}. Taylor and Müller-Eberhard⁴ observed that blocking either fibrinogen or γM-globulin with specific antibody prevented normal retraction and lysis of dilute whole-blood clots prepared by the technique of Fearnley et al.⁴. Because platelets are also necessary for a normal response⁴, their studies suggested that the fibrinogen and γM-globulin adsorbed onto the platelets play an essential part in the process.