In rat kidney, the changes in concentrations of nucleotides and their derivatives during ischemia induced by renal artery ligation was measured quantitatively with high performance liquid chromatography (HPLC). After the ligation of renal artery for 60minutes, the concentrations of the nucleotides and derivatives to 80.7±18.39 µg (p<0.01); ATP, 307.2±56.68 µg to 47.6±5.95µg (p<0.01); ADP+AMP, 227.1±7.98 µg to 61.4±3.92 µg (P<0.01); NAD+, 217.9±4.49 µg to 126.6±10.44 µg (P<0.01); GTP, 202.5±23.76 µg to 117.7±14.24 µg (P<0.05); GMP, 54.5±9.03µg to 23.7±0.46 µg (p<0.05), and inosine, 16.6±3.45 µg to 7.8±0.87 µg (P<0.05). But hypoxanthine and xanthine were significantly increased from 113.0±15.58µg to 159.7±12.97µg (P<0.05) and from 87.7±6.77µg to 173.1±12.52µg (P<0.01). In ischemic kidney, concentration of ATP was decreased to 39.9% of control at 10 minutes, 19.8% at 30 minutes, and 15.5% at 60 minutes, and ADP+AMP were decreased to 70.3% of control at 10 minutes, 67.3% at 30 minutes, and to 27.0% at 60 minutes, but hypoxanthine and xanthine were increased to 121.5% and 127.1% at 10 minutes, 126.0% and 174.4% at 30 minutes, and 141.4% and 197.3% at 60 minutes. Total adenosine nucleotides were decreased to 20.3% of control during 60 minutes of ischemia, but hypoxanthine and xanthine were increased to 157.5% of control. These results suggest that the changes in the concentration of nucleotides and their metabolic derivatives are useful indices of the extents of tissue ischemia in rat kidney.