A study has been made of the effect of changes in intestinal distention upon the blood pressure of a dog whose vagosympathetic trunks are divided and common carotid arteries ligated on both sides of the neck, and whose splanchnic nerves are divided. The blood pressure in such an animal would be expected to vary inversely with the degree of splanchnic congestion induced by the distention of the gut. The only factor difficult to control in such an animal is the contractility of the intestinal muscle, which in responding to a rise in intra-intestinal pressure may contract tightly, rendering the intestine anemic, and, by the consequent increase in peripheral resistance to the blood flow, causing a rise in blood pressure. This pressor effect obtained in 5 dogs in which the whole small intestine, ligated at both ends as a closed loop, was distended with air. In 5 dogs and 3 cats, however, the intestine remained passive under distention, and became distinctly cyanosed at an air pressure of 60-90 mm. of mercury, and the blood pressure of these animals exhibited at once a sharp fall of from 20-90 mm. of mercury within half a minute. Release of this intestinal distention after a period of from 5 minutes to 7 hours was followed by a return of the color of the bowel to normal, and by a rapid rise of blood pressure to its original level or beyond it. In a further series of 5 dogs, prepared in the same way, the distention was maintained from 6-18 hours. Release of the distention was again followed by return of the bowel to a normal color, but in 3 animals, instead of the rise in blood pressure which occurred in the previous series, a sharp fall was observed. In one of these 5 dogs indeed the blood pressure, perfectly stable before release of the distention, fell progressively after release till the animal's death 7 1/2 minutes later. In 2 other animals distended for more than 18 hours, and in one animal distended for only 12 hours, the bowel failed to resume its normal color after collapsing and remained cyanosed. In these dogs there was no alteration in the blood pressure.