methods of cooling blood platelet suspensions which can be stored and preserved for extended periods of time . the normal morphology of platelets and their ability to function are substantially maintained . the steps include preparing a platelet suspension having blood platelets , a carbohydrate and at least one biocompatible polymer to assist in stabilizing platelet membranes . the platelet suspension may be cooled to a temperature of less than approximately 10 degrees c . at a rate of cooling greater than 1 degree c ./ min . the platelet suspension may be kept at a storage temperature ranging from approximately − 1 to 6 degrees c . additionally , methods are provided for maintaining the biological activity of blood platelets . platelet suspensions may be initially prepared which include platelets , sucrose , verapamil , magnesium chloride and a biocompatible polymer . cooling of the platelet suspension may be followed at a cooling rate ranging from approximately 1 to 12 degrees c ./ min or faster to a temperature below 10 degrees c . the cooled platelet suspension may be thus stored at a storage temperatures as high as 6 degrees c .