Changes in plasma amino acids, 24-h nitrogen balances, and resting metabolic expenditures (RMEs) were measured in 10 geriatric patients (aged 70-92 y) with hip fracture 1 d after surgical fixation during both a 24-h fasting state and while receiving total peripheral parenteral nutrition (TPPN) for 24 h at 1.5 g amino acids.kg-1.d-1 and 29-30 kcal.kg-1.d-1 and compared with 19 healthy volunteer subjects (aged 70-84 y). RME and 24-h urinary nitrogen losses were also elevated in the trauma patients during both fasting and TPPN. Positive nitrogen balances were evident in both groups during TPPN. Plasma total amino acid concentration was significantly lower in the trauma patients because of lower plasma concentrations of the nonessential amino acids. Phenylalanine and methionine concentrations were significantly higher and lysine lower in the trauma group. In addition, evaluation of the essential amino acid ratios after fasting and TPPN reveal that there are no limiting amino acids during TPPN.