The cellular levels of adenine nucleotides and their metabolites in ischemic rat liver were assayed by high pressure liquid chromatography with high theoretical plate numbers. The method was sensitive enough to measure all the metabolites in about 1 mg of tissue, and to examine changes in their levels in a single liver in ischemia. In ischemia the cellular level of ATP decreased rapidly. Concomitantly there was a transitory increase in AMP, followed by its degradation to allantoin via adenosine with accumulation of all species of purine catabolites. NAD was also degraded gradually with concomitant accumulation of nicotinamide. Thus, the level of total adenine nucleotides decreased during ischemia and the amount of this decrease ws equal to the sum of the amounts of catabolites produced. The ATP level was rapidly restored on recirculation after an ischemic period of less than 15 min. However, recovery of the ATP level was depressed by prolonged ischemia and was not observed after an ischemic period of 2 h. Intermediate purine catabolites that accumulated in ischemia were also cleared during recirculation either by their removal in the blood flow or by further oxidative degradation, but they were not salvaged for reuse until the cellular level of ATP was restored. Administration of allopurinol resulted in marked accumulation of hypoxanthine in ischemic liver, but neither this drug nor chlorpromazine had any appreciable effect on recovery of the ATP level during recirculation.