Renal ischaemia produced by clamping of the blood vessels in situ for periods of 10 to 150 minutes resulted in a progressive depletion of the total content of adenylates in the kidney tissue (sigma ATP, ADP, AMP). Initial dephosphorylation of ATP and ADP, resulting in further catabolism of AMP to hypoxanthine and xanthine, accumulated in the ischaemic tissue. The postischaemic ability of the kidney tissue to functional regeneration was in correlation with the ischaemic adenylate loss (r = +0.94, P less than 0.001) as well as the accumulation of hypoxanthine and xanthine (r = -0.90, P less than 0.001). The initial adenylate resynthesis rate was constant during recovery (0.5--0.8 mumol/g . h-1), independent of the duration of the preceding ischaemia. Determination of the postischaemic adenylate regeneration thus gave no additional prediction of the reversibility of the ischaemic parenchymal damages.