The present study was done to determine: (1) regional (cortex, red medulla and papilla) changes in ATP, ADP and AMP resulting from periods of ischemia of 30-300 s; (2) whether ischemic changes in adenine nucleotides or lactate were modified by hypertonic saline loading, and (3) whether adenylate kinase activity was present in each region. Ischemia led to changes in all three adenine nucleotides which were characteristic for each region. In cortex, there was a major decrease in ATP, increase in AMP and a small transient increase in ADP. In red medulla there were slower changes in ATP, ADP and AMP. In papilla, ATP decreased slightly and ADP, as opposed to AMP, accumulated. Hypertonic saline loading increased the rate of ATP decrease and AMP accumulation, most markedly in red medulla. Lactate concentration rose similarly in control and hypertonic saline studies. Adenylate kinase activity was found to be present in each region. In conclusion: (1) the rate of change of all three adenine nucleotides differs among the three renal areas studied; (2) increases in renal transport work, associated with hypertonic saline loading, are reflected in an increase in the rate of ATP decay during ischemia; (3) anaerobic metabolism, as indicated by tissue lactate concentration, is not altered by hypertonic saline loading, and (4) the failure of AMP to accumulate in papilla is not due to the absence of adenylate kinase.