An experimental study was performed to determine the effects of a BCAA enriched amino acid solution on sepsis in rats. After sepsis had been induced in male Wistar rats by caecal ligation and puncture the animals were divided into four groups according to the amino acid solutions infused: Group B-I, a solution containing no amino acid; Group B-II, a commercially available solution containing 21.1% branched chain amino acids (BCAA); Group B-III, a solution containing 38.7% BCAA and Group B-IV, that containing BCAA only. The control group of the animals received simple laparotomy and infusion without amino acids. Infusion was continued for 96 hours after the operation and all the solutions had the same caloric and nitrogen value. Group B-I had a plasma aminogram peculiar to sepsis; a significant rise in the concentration of the total 17 amino acids (TAA), BCAA and aromatic amino acid (AAA) together with a decrease in the BCAA/AAA ratio. Furthermore, the arterio-venous difference (AV-D) of AAA and BCAA showed a large negative value. In the three groups infused with amino acids, only Group B-III showed a significant improvement in the survival rate and nitrogen balance compared with Group B-I. Moreover, not only did the concentration of TAA and AAA significantly decline, but also the BCAA/AAA ratio increased. Therefore, the abnormal aminogram in sepsis tended to return to the control level. In Group B-IV despite the significant decrease of the peripheral TAA, no improvement in plasma aminogram, nitrogen balance or survival rate were shown. In Group B-II, in addition to the persisting plasma aminogram changes and peripheral efflux of amino acids, no improvement of survival rate were noted. Therefore, it was concluded that an amino acid composition richer in BCAA and lower in both AAA and SCAA is beneficial in the treatment of sepsis.