The nutritional influence of branched chain amino acids (BCAA) and lipids in surgical stress was examined after 70% hepatectomy in rats. Two types of elemental diet (ED) were given through the gastrostomy tude for 7 days. Group A : ED containing 33% BCAA and 30% lipid (medium chain triglycerides 8.5g＋soy bean oil 1.5g/300 kcal). Group B : ED containing 17% BCAA and 1.5% lipid (soy bean oil 0.49g/300 kcal). Up to the 7th postoperative day, the excretion of nitrogen into urine decreased in group A, but no change occurred in group B. Up to the 5th postoperative day, molar ratio of 3MH to creatinine in urine in group A decreased more rapidly than in group B. Plasma concentration of albumin in group A was higher than in group B on the 7th postoperative day. Fischer ratio was significantly higher in group A than in group B on the 7th postoperative day. Both plasma and muscle levels of Tyr, Met and Gln were higher in group B than in group A, Glu and Ala were lower in group B than in group A. Essential fatty acid deficiency occurred more severely in group B than in group A. While fatty livers were microscopically observed in some livers in group B, there were few fatty deposits in group A.