The effect of the cyclooxygenase inhibitor indomethacin (3.4 mg/kg/24 hr) on systolic blood pressure (PB) and plasma-renin-activity (PRA) was evaluated in normotensive and renovascular hypertensive rats receiving either a normal or low salt diet. Indomethacin reduced PRA in normal and hypertensive animals on both low and normal salt intake. Indomethacin furthermore, decreased BP in animals on low sodium diet but increased PB in sodium repleted rats. These data suggest that the effect of indomethacin on rat BP may depend on the state of extracellular volume and PRA.