The ability to regenerate the adenylate content in renal tissue appears to fail in rabbit kidney grafts, cold stored for 24 hours. The post implantational adenylate regeneration which did not occur, took place within the first lo minutes of re-established circulation. Thirty and sixty minutes of re-vascularization did not give any additional adenylate synthesis. The presence of adenosine (2.5 mM) in the preservation fluid, and that taken up by the kidney tissue during in vitro storage, brought about a significant increase in adenylate regeneration during the postimplantational period, independennt of a parallel increase in renal blood flow, and irrespective of the fact that adenosine did not show any adenylate preserving effect in vitro. The present results suggest that in long-term stored rabbit kidney grafts there occurs a relative postischaemic lack of intracellular available purine precursors. Owing to the filtration inhibiting effect of adenosine a study of the correlation between kidney function and adenylate regeneration was not possible.