The isolated abdominal aorta was perfused in 6 cats and 2 dogs, and perfusion of the isolated superior mesenteric arterial system was performed in another 6 cats. In every experiment, wide variations in perfusion pressure produced no alterations in the systemic pressure, although it was responsive to manipulation of the carotid pressure. A comparison of the systemic pressure responses to mesenteric artery occlusion and to carotid artery occlusion prior to and following (1) high spinal transection in 2 cats or (2) venous perfusion of sodium thiopental in 3 cats showed an obliteration of the responses to carotid occlusion while the systemic response to oclusion of the mesenteric artery persisted. The results indicate that the systemic responses seen during mesenteric artery occlusion are probably caused by mechanical diversion of blood from one vascular bed to another and do not represent true reflex responses. The observations indicate that mesenteric pressure receptors do not contribute significantly to the reflex regulation of the systemic blood pressure.