The effects of atrial natriuretic polypeptide (ANP) on renal function were examined in renal wrap hypertensive rabbits and sham operated rabbits. 2. ANP (2 micrograms/min) induced hypotension, but did not produce significant diuresis, natriuresis or change in the glomerular filtration rate (GFR) in renal wrap hypertensive rabbits (n = 8). 3. In sham operated normotensive rabbits (n = 4), ANP induced significant diuresis (230%) and increased GFR by about 40%. 4. Thus, ANP was markedly less effective in the impaired kidneys of renal wrapped rabbits than in normal kidneys.