The ratio of acetoacetate to 8-hydroxybutyrate (ketone body ratio) in the blood may reflects the mitochondrial free NAD+/NADH ratio in the liver. Also arterial ketone body ratio will reflects the energy status of the hepatocytes, because mitochondrial free NAD+/NADH ratio is closely related to oxidative phosphorylation. Arterial ketone body ratio and osmolal gap, the difference between measured osmolality and calculated osmolality, were measured 30 min after the induction of hemorrhagic shock with mean arterial blood pressure at 40 mmHg in ten rabbits. Arterial ketone body ratios decreased significantly (p<0.05) from 0.74+/-0.17 to 0.38+/-0.09 and osmolal gap increased significantly (p<0.05) from 17.7+/-5.9 mOsm/Kg to 32.8+/-12.3 mOsm/Kg at 30 min after the induction of hemorrhagic shock. These results suggest that in hemorrhagic shock, decreased arterial ketone body ratio which reflects the inhibition of the TCA cycle is associated with increase of osmolal gap.