The left kidneys of anaesthetized, heparinized rats were subjected to a 60-min period of warm ischaemia in vivo and perfused in situ with either isotonic saline, human plasma protein fraction, Perfudex® (Pharmacia), 20% mannitol or Sacks’ solution at 37 °C. A second similar series were perfused at 4 °C. One further group had autologous arterial blood perfusion at body temperature. Immediate contralateral nephrectomy was done and function was assessed by regular plasma creatinine estimation and survival (life supporting function). Control groups consisted of unilateral nephrectomy alone, 45 or 60 min of ischaemia with immediate contralateral nephrectomy. The only significant improvement in function in the experimental groups when compared to the 60-min ischaemia control group was seen following perfusion with isotonic saline at 37 °C (p < 0.05) and with autologous arterial blood perfusion (p < 0.005). Renal function following this period of warm ischaemia was not significantly improved by any of the other perfusates tested.