Glucose and energy metabolism in rat liver after ischemic damage was investigated by in vivo 31P NMR spectroscopy, 1H-detected 13C NMR spectroscopy, and in vitro 13C NMR spectroscopy using [1-13C]glucose as a tracer. Arterial ketone body ratio (AKBR; acetoacetate/beta-hydroxybutylate) and oxygen consumption of isolated mitochondria were also examined to evaluate hepatic function. The rats were divided into three groups: (A) without ischemia, (B) 10-min ischemia, and (C) 30-min ischemia. ATP was almost depleted at 10 min of ischemia and recovered after reperfusion, but the recovery was not complete. The recovery after 30-min ischemia was smaller than that after 10-min ischemia. [13C]Glucose was infused immediately after the reperfusion, and in vivo 1H-detected 13C NMR demonstrated sequential glucose incorporation into the liver. However, the incorporation depended on the blood sugar levels and did not reflect hepatic function. In vitro 13C NMR disclosed the glycogen C-1 signal in the nonischemic group and alanine C-3 and lactate C-3 signals in the ischemic groups. The intensity of glycogen was correlated positively (r = 0.648, P = 0.002) and those of alanine and lactate were correlated negatively (r = -0.831, P < 0.005 and r = -0.710, P = 0.005, respectively) to the ATP levels as measured by in vivo 31P NMR. These results suggested that ATP level participates in glycogenesis and gluconeogenesis in the liver. The AKBR and oxygen consumption of isolated mitochondria were the highest in the 10-min ischemia group, which might reflect mitochondrial compensatory response to the decreased ATP level.