The role of the adrenergic nervous system in the renal vasoconstriction by acetylcholine (ACh) in indomethacin (INDO)-treated dogs was examined in dogs pretreated with reserpine (R) or in dogs receiving an intrarenal infusion of phenoxybenzamine (P). In INDO-treated dogs which also received treatment of R (0.5 mg/kg/day, I.M. for 2 days) or P (0.5 mg/kg followed by 190 Mug/min), 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 increase in RS. It is concluded that ACh produces renal vasoconstriction in INDO-treated dogs by mechanism(s) other than an increase in the release of norepinephrine from renal sympathetic nerves.