Rats subjected to laparotomy and handling of the liver were starved for 48 h, starting either immediately after surgery or 48 h later. Surgery enhanced the rise in plasma non-esterified fatty acid concentrations after starvation without affecting the responses of blood or liver ketone bodies. Thus in surgically stressed rats, blood and liver ketone body concentrations were inappropriately low for the blood fatty acid concentrations. In the control rats, starvation increased hepatic carnitine concentrations, mainly through increases in short-chain acylcarnitine. Surgical stress decreased or abolished these increases. This may possibly contribute to the blunted ketonaemic response observed after surgery.