Bilateral renal artery stenosis was established in 35 rats. In 23 rats with bilateral renal artery stenosis alone, systolic blood pressure was sustained at hypertensive levels. Simultaneous diversion of the renal venous efflux into the portal system in 12 of them was followed by prolonged maintenance of normal systolic blood pressure after the initial rise during the first week. Furthermore no elevations in blood pressure followed either caval portal bypass alone or sham operation alone. The results of earlier experiments in the dog have thus been confirmed in animals of another species. Hepatic inactivation of renin or angiotensin following diversion of renal venous efflux into the liver is suggested as the mechanism of prevention of renovascular hypertension by caval portal shunt.