The responses to 48 h of renal artery stenosis were compared in uninephrectomized, chronically-instrumented dogs with or without inhibition of angiotensin II (AII) formation by enalapril. Mean arterial pressure rose by an average of 29.9 mmHg (s.e.m. 3.5) in untreated dogs and by 14.5 mmHg (s.e.m. 2.8) in enalapril-treated dogs over the two days of stenosis. Renal artery stenosis reduced glomerular filtration rate (GFR) by 49% (s.e.m. 9) in untreated dogs and by 86% (s.e.m. 8) in enalapril-treated dogs. Compared to untreated dogs, enalapril-treated dogs also had lower renal artery pressure distal to the stenosis, drank less water and had larger rises in plasma K+ following renal artery stenosis. There were no differences in renal blood flow or urinary Na+ excretion in the two groups of dogs. Thus blockade of AII production did not prevent hypertension occurring in response to renal artery stenosis, but the rise in blood pressure was only about half that which occurred in normal dogs and GFR was much more severely reduced.