The influence of intravenously administered L‐carnitine on lipid‐ and nitrogen‐metabolism was studied during total parenteral nutrition of piglets (mean weight 4077 g; n = 9). The infusion protocol was divided into three isocaloric and isonitrogenous 48‐hr periods. Amino acids (3 g/kg day) were administered throughout all three periods: 140 cal/kg/day were given as nonprotein calories, consisting only of glucose during period 1; during periods 2 and 3, an amount of glucose calorically equivalent to 4 g fat/kg/day was substituted with a lipid emulsion, and L‐carnitine (1.5 mg/kg/day) was added in period 3. Key parameters of fat‐ and nitrogen‐metabolism were determined during the entire regime. Indirect calorimetry was performed and the respiratory quotient calculated during all three periods. The results demonstrate a more effective lipolysis and oxydation of fatty acids during L‐carnitine supplementation. These changes produce an increased energy gain from exogenously administered fat and a distinct improvement in nitrogen balance.(Journal of Parenteral and Enteral Nutrition8:9–13, 1983)