Twenty thermally injured patients who could not tolerate enteral nutrition support were randomized to receive parenteral nutrition (PN) with either modified amino acids (MAA) or standard amino acids (SAA). There was no significant difference between groups for age, sex, weight, percent BSA area burn, percent third-degree burn, or operative procedures. N balance (NB) was measured and serum was harvested for circulating fibronectin (Fn), somatomedin-C/insulin-like growth Factor I (Sm-C), prealbumin (PA), and retinol-binding protein (RBP) analysis on days 1, 4, 7, 14, 21, and 28 of PN. The patient groups received similar doses of PN for a similar number of days. Fn did not change significantly from baseline in either group and there was no significant difference between groups. Sm-C increased significantly from baseline at day 7 in the SAA group and in both groups on day 14, but there was no significant difference between groups. PA and RBP increased significantly from baseline on day 7 in the MAA group and in both groups on days 14, 21, and 28. RBP was significantly higher in the MAA group only on day 21, and there was no significant difference between groups for PA. NB increased significantly from baseline for all study days; however, there was no significant difference between groups. PN in thermally injured patients significantly improves NB and increases visceral protein concentrations. However, there appears to be no difference between PN with MAA or SAA.