A response of the aortic smooth muscle to reduction in venous return was demonstrated previously. The present experiments were performed to determine whether these responses were of a reflex origin rather than being attributable to viscoelastic mechanisms. Viscoelastic mechanisms could not account for changes seen in the aortic pressure diameter relationship curve. On the other hand, it was demonstrated that the response was abolished by eliminating sympathetic input to the aorta via spinal cord transection. This and other evidence demonstrate beyond doubt that the aortic response to reduction in venous return is of neurogenic origin and constitutes a well-integrated reflex. However, experimental evidence is presented which clearly indicates that the receptors for the aortic smooth muscle response are not located in either the carotid sinus or aortic arch but must be located elsewhere in the system.