Age-associated decrease in lean body mass may lead to varied responses to severe trauma. Hypoaminoacidemia is generally common among trauma victims. We measured the plasma free amino acids in the early "flow," ie, catabolic, phase of injury in 9 elderly (aged 61-81 y) and 13 young (aged 20-38 y) traumatized patients. Postabsorptive control samples were obtained from 8 elderly and 10 young volunteers. The results were analyzed for age-related responses to major trauma. Older healthy control subjects showed a decrease in total amino acids, essential amino acids, proline, histidine, taurine, and cystine. The hypoaminoacidemia was less pronounced in geriatric trauma, mainly because of a larger decrease in nonessential amino acids in young trauma victims. Significant decreases in arginine and methionine and increases in ornithine and citrulline concentrations were seen in geriatric trauma. These results suggest a sluggish protein metabolic response to trauma in elderly individuals, which should be considered in their nutritional management.