Plasma renin concentration (PRC), renal blood flow (RBF) and renin secretion rate (RSR = renal veno-arterial PRC difference multiplied by renal plasma flow) were measured before and after a period of hypothermic renal ischaemia in seven patients undergoing surgery for renal calculi. After hypothermic (10-15 degrees C) ischaemia (duration 36 to 71 min) the temperature rose to 37 degrees C within 4 min, while RSR decreased transiently in the posthypothermic postocclusive period. Maximal decrease in RSR (-65%) was found 6 min after re-establishment of the renal perfusion, and 30 min later RSR was similar to the prehypothermic, preocclusive value. RBF decreased in the same period, while mean arterial blood pressure and renal oxygen uptake were unchanged. The results are compatible with a reversible depression of the release of renin in the postocclusive, posthypothermic human kidney.