The present study compared the effects of ATP-MgCl2 or ATP-Na2 administration on renal function and cellular metabolism following renal ischemia in rabbits. Following 100 min of ischemia, the blood flow to the kidney was allowed to reestablish itself, and the rabbits received either saline, ATP-MgCl2 (17.5 mumole/kg each), or ATP-Na2 (17.5 mumole/kg) intravenously. ATP-MgCl2 administration following ischemia significantly accelerated the recovery of renal function. However, administration of ATP-Na2 failed to show any beneficial effect on the recovery process. The changes in renal cellular ketone body ratio (acetoacetate/beta-hydroxybutyrate), energy charge, and pyruvate/lactate indicated that ATP-MgCl2, but not ATP-Na2, reversed ischemically induced impairment in renal cellular metabolism. Reduction in the renal blood flow caused by ischemia was also improved with ATP-MgCl2 treatment. These results indicate that ATP should be given in the form of ATP-MgCl2 for it to be effective following renal ischemia. The results also suggest that the salutary effect of ATP-MgCl2 following renal ischemia could occur through the improvement of cellular metabolism and concomitant improvement in tissue blood flow.