A quantitative bleeding time test (cold-tolerance test) is described in which the bleeding site is exposed to different temperatures. No difference in bleeding time and blood loss was seen between 33° C and 25° C. When the temperature of the wound was decreased to 16° C or below, bleeding increased significantly in all normal persons and in those with coagulation abnormalities, except for two patients withvon Willebrand's disease in whom bleeding actually dimniished. Patients with congenital deficiencies of factor VIII, IX, or X had normal Ivy bleeding times but remarkably prolonged bleeding times at 16°C. After transfusion of cryoprecipitate into one patient with classic hemophilia, the bleeding time at 16° C returned to normal. Abnormal bleeding times at 16°C also were found in one patient taking aspirin and in one taking phenobarbital.