An isolated perfused rat kidney has been used to determine the response to prolonged warm ischaemia and to examine renal preservation procedures. All measurements of function declined to near zero after 90 min of warm ischaemia. Measurement of total sodium reabsorption (TNa) was the most sensitive indicator of renal damage. Inosine was without effect on subsequent renal function after 60 or 90 min of warm ischaemia, or after 24 hr of cold ischaemia. Surface cooling or hypertonic citrate solution, in the cold or at 37 C, significantly improved renal function, and their use in clinical renal preservation rather than that of inosine was supported by the present results.