The effects of ketone bodies and glucose on nitrogen balance and liver protein synthesis were studied in rat after experimental trauma. Energy was delivered intravenously as either monoglyceryl acetoacetate (MA; 87.5% of total energy input) or glucose (G). The isocaloric infusions (132 kcal/kg/day) were started after recovery from anaesthesia and continued for 2 days. The liver protein synthesis was then measured in vitro by perfusion with 14C-leucine. The infusion of MA resulted in a more negative cumulative nitrogen balance (MA: -2.31 +/- 0.26 g N/kg, G: -1.32 +/- 0.43 g N/kg/48 h; mean +/- SD) and liver protein synthesis (MA: 43.4 +/- 17.2, G: 71.1 +/- 15.2; arbitrary units, mean +/- SD). The results indicate no benefits from MA during the immediate post-traumatic period.