1. Inhibition of prostaglandin synthesis by indomethacin induced an increase in blood pressure which did not occur when rats were bilaterally nephrectomized.
2. The blood pressure effect was related to the state of sodium balance and thus to the activity of the renin-angiotensin system.
3. Indomethacin induced a decrease in renal blood flow.
4. Angiotensin receptor blockade with Sar1-Ala8-angiotensin II blunted the blood pressure effect and prevented the renal haemodynamic changes induced by indomethacin.