This study examined the effects of total parenteral nutrition (TPN) enriched with branched-chain amino acids (BCAAs) on metabolite levels of carbohydrate and protein metabolism in septic rats. Results also were obtained for standard amino acid hyperalimentation (conventional TPN). Septic peritonitis was induced in rats by cecal ligation and puncture. Two different experimental models were tested. In one, the two kinds of TPN were administered to the operated rats during the progress of sepsis (the septic phase). In the other, TPN was started immediately after surgical removal of the focal cecum (the recovery phase). The conventional and BCAA-enriched TPN solutions were isocaloric and isonitrogenous except that the percentage of BCAAs in the total amino acids by weight was 35.8% in BCAA-enriched TPN and 20.9% in conventional TPN. On the fifth postoperative day, TPN was discontinued, the animals were killed, and samples of arterial blood, liver, and rectus abdominis muscle were taken. BCAA-enriched TPN had a significant effect on nitrogen balance and survival rate in the septic phase model, and on muscle adenine nucleotide content in both models. Other metabolites showed similar changes in the two TPN groups. These results indicate that BCAA supplement in TPN improves nitrogen balance and peripheral cellular energy status and is thus clinically beneficial in preventive therapy for increased catabolism.