The role of the sympathetic nervous system for the regulation of intraocular pressure has been studied by many investigators, with varied and contradictory results. Reviews of the literature have been made by Thiel,11 Duke-Elder,2 Magitot,9 and, more recently, Jaffe6 and Weinstein.12 At the time of those studies attention was focused on intraocular pressure rather than on aqueous flow, since no suitable techniques for measurement of aqueous flow were available. A change in the intraocular pressure of short duration can be caused by many different factors—for instance, a change in the blood volume of the eye. On the other hand, only three factors, namely, the rate of aqueous inflow, the facility of aqueous outflow, and the episcleral venous pressure, can determine the long-continued level of intraocular pressure. The purpose of the present work was to study in rabbits the effect of extirpation of the superior sympathetic