1. The effect of a 4 h period of bilateral hind limb ischaemia on the concentrations of ketone bodies in blood and liver of post-absorptive and starved rats has been investigated.
2. The concentration of total ketone bodies in the blood did not change after injury in post-absorptive rats, but fell after injury in starved rats; the blood β-hydroxybutyrate/acetoacetate ratio fell after injury in both post-absorptive and starved rats.
3. Apart from a transient increase in fed rats, the hepatic β-hydroxybutyrate/acetoacetate ratio did not change after injury in post-absorptive or starved rats until the terminal stages, indicating adequate hepatic oxygenation during the early response to injury.
4. In control post-absorptive and starved rats the concentration of liver total ketone bodies was correlated with that of plasma non-esterified fatty acids; in post-absorptive rats the liver ketone body concentration rose after injury and was higher than would be predicted from the regression line for these controls, suggesting increased ketogenesis compatible with inhibition of complete oxidation of non-esterified fatty acids after injury. In contrast, in starved rats the liver total ketone-body concentration did not change after injury.