1. The functions of right and left kidneys were measured immediately preceding, during and for 4 h after 45 min occlusion of the blood supply to the left kidney.
2. The blood supply was occluded by placing a clamp around the renal artery near to the aorta (group 1), near to the renal hilus (group 2) or by clamping the renal pedicle after prior separation of the kidney from perirenal tissue (group 3).
3. During ischaemia right kidneys had increased urine flow rates and excretion of sodium and water, but inulin clearances (CIn) remained unchanged.
4. After ischaemia left kidneys were isosthenuric with depressed CIn.
5. Occlusion of the renal artery alone resulted in non-oliguric kidneys in which CIn was reduced to 10% and 1% respectively for groups 1 and 2.
6. The most severe damage to function was seen in the kidneys of group 3 which were oliguric and in which CIn was depressed to 0.1% of the pre-ischaemic value.
7. It is concluded that the pedicle clamp method produced complete renal ischaemia and the most severe damage to function. Occlusion of the renal artery produced incomplete ischaemia and a less severe fall in function which depended upon the site of occlusion.