The role of the renin-angiotensin system in the renal vasoconstriction by acetylocholine (ACh) in indomethacin (INDO)-treated dogs was examined in dogs receiving infusion of either saralasin, an angiotensin II blocker (intrarenal), saralasin and phenoxybenzamine (intrarenal) or propranolol (I.V.) In INDO-treated dogs receiving an infusion of saralasin alone or in combination with phenoxybenzamine and propranolol, renal arterial infusion of ACh produced an initial rise in sodium excretion (UNaV) and renal plasma flow (RPF) with no change in renin secretion (RS). This was followed by a fall in UNaV and RPF with an increase in RS. It is concluded that ACh produces renal vasoconstriction in INDO-treated dogs by mechanism(s) other than an increase in the activity of the renin-angiotensin system.