The intraperitoneal administration of thrombin increased the bleeding due to the amputation of the tail in the rat (average blood loss 4.6 ml.). The intravenous administration of ellagic acid in thrombin-injected rats reduced the average blood loss to 0.6 ml. This value was slightly more than the average blood loss noted in animals given only ellagic acid (0.2 ml.). Both these figures were much less than the average blood loss observed in control animals (3.2 ml.).