The interaction of the prostaglandin and renin-angiotensin systems on blood pressure and renal function was studied in conscious rabbits following mild (6 ml/kg) or moderate (15 ml/kg) hemorrhage. One hour following the injection of the prostaglandin synthetase inhibitor indomethacin (Indo) plasma renin activity (PRA) was significantly lower than the values in control animals. Two hours following hemorrhage, the increase in PRA was very similar in the Indo and control animals. Renal plasma flow (RPF) was not affected by Indo. Glomerular filtration rate (GFR) was significantly lower in the Indo group following moderate hemorrhage. Interruption of the renin-angiotensin system with the converting enzyme inhibitor (CEI), captopril, resulted in similar hypotensive responses in the Indo and non-Indo groups. The marked PRA increase induced by this agent also was not influenced by Indo. The CEI increased RPF and decreased renal vascular resistance (RVR) in the mild hemorrhage animals. However, in the moderate hemorrhage group the RPF changes were variable and RVR tended to increase, especially in the Indo group. GFR fell significantly following captopril in both Indo and non-Indo animals after moderate hemorrhage. The results indicate that prostaglandin inhibition lowers basal PRA levels but that the renin response to hemorrhage and captopril are not prevented. Indo also did not alter the hypotensive response to CEI, suggesting that prostaglandins do not play a major role in this effect. The magnitude of the hemorrhagic stress influences the renal responses to inhibition of the prostaglandin or renin-angiotensin systems in the conscious rabbit.