IN RECENT YEARS it has been recognized that thrombocytopenic hemorrhage may occur from massive transfusion with stored whole blood, from toxic or immunologie causes, or from the depression of platelet production following radiation or chemotherapy. Restoration of the coagulation mechanism by replacement of viable platelets will effectively control the bleeding. In the event of nuclear warfare, the fatality rate from tlirombo- cytopenia would be high. It is obvious that a method to store blood platelets for long periods of time should be developed in order that coagulation deficiencies secondary to thrombocytopenia may be treated rapidly and effectively. These needs prompted us to report a series of experiments in 1958 in which canine platelets were frozen in the presence of glycerol and stored for periods up to 4 months at -79° C. (-110.2° F.). The preservation of clot retracting ability following thawing indicated that at least a portion of the platelets