It has been previously shown that it is possible to produce the syndromes of reversible shock,1 irreversible shock,2 pseudomembranous enteritis,3,4 lower nephron nephrosis,5,6 and acute pancreatic necrosis7 by means of the intra-aortic injection of incompatible (human) blood into dogs. Incompatible blood has been shown to cause intravascular clotting,9-12 and clotting appeared to be the primary factor involved. However, it seemed desirable to repeat this work utilizing pure thrombin to rule out possible other effects of such a protean substance as human blood. Accordingly, the following experiments were set up to duplicate the above experiments,1-7,10-12 substituting pure thrombin in normal saline for human blood. Materials and Methods Thirty mongrel dogs of both sexes were anesthetized with sodium pentobarbital. Bilateral femoral artery catheters were inserted up to the level of the thoracic aorta. One of these was used to measure mean aortic blood pressure, the