There are conflicting reports with regard to the antihypertensive effectiveness of interleukin-2 in the spontaneously hypertensive rat Recently, the original claim of a normalization of arterial pressure in the spontaneously hypertensive rat after a single administration of interleukin-2 has been disputed. Therefore, the present study was performed to determine whether the administration of interleukin-2 was effective in attenuating both the development and maintenance of hypertension in the spontaneously hypertensive rat Both young prehypertensive spontaneously hypertensive rats and adult spontaneously hypertensive rats with established hypertension received a single subcutaneous dose of 5,000 units/kg human recombinant interleukin-2. Arterial pressure was monitored at weekly intervals in both control and treated animals by the tail-cuff technique. Interleukin-2 administered as a one time single injection had no effect on the development of hypertension in the young animals or on the maintenance of hypertension in the adult animals. Interleukin-2 also was administered as a continuous infusion via osmotic minipumps at dose levels of 5,000 and 50,000 units/kg/wk to both young and adult spontaneously hypertensive rats. Continuous administration of interleukin-2 also had no effect on the development or maintenance of spontaneous hypertension. Therefore, this study firmly demonstrates that interleukin-2 has no effect on the onset or maintenance of hypertension in the spontaneously hypertensive rat