1. The basal oxygen consumption, respiratory quotient, blood flow, blood pressure, and the changes in concentration of the arterial blood were determined in suprarenalectomized dogs (a) when receiving injections of cortical extract (Swingle-Pfiffner), (b) during suprarenal insufficiency induced by withdrawal of the injections, and (c) during the period of recovery brought about by resumption of extract injections. 2. Reasons are advanced for the view that the hemoconcentration which occurs is probably due to loss of fluid through the kidneys, rather than by increased capillary permeability and loss into the tissues, or by loss through the gastrointestinal tract. 3. The loss of fluid from the plasma and tissues will explain the symptoms which follow withdrawal of injections of the hormone, as well as the fatal outcome. The assumption that the suprarenal cortex or its hormone has a detoxifying action upon some product of metabolism is thus rendered unnecessary.