Two groups of rats (group 1 and 2) were normal control and liver injury group induced by 14mg of dimethylnitrosamine per kg body weight per os. A half of group 1 and 2 (3 days after the administration of DNA) received 6mg of 15NH4Cl per 100g body weight intraperitoneally. The other halves of group 1 and 2 received 8.4mg of 15N-glycine per 100g body weight. 15N in plasma albumin and urea was determined at one and three hours after the injection. The incorporation of the isotope into plasma albumin of the rats received 15N-NH4Cl was lower in group 2 than group 1. The incorpolation into urea was higher in group 2 than group 1. In the rats received 15N-glycine, the incorporation of 15N into albumin was higher in group 2 than group 1, and into urea of group 1 and 2 was the same. Four groups of 5 rats each, weighing 240g, were fed daily with 10g of a synthetic diet that had no protein. Group 1 received 0.8g casein daily over the fundamental diet, and group 2 received 0.8g more starch instead of casein. Group 3 received 30ml of amino acid mixture that contained amino acids in amount and composition similar to that of 0.8g casein intraperitoneally, and group 4 received the same mixture per os. Four weeks after the feeding, all the rats were administrated 8mg of 15N-NH4Cl per 100g body weight, and 15N in the plasma albumin and urea was determined hourly for 4 hours. No weight loss or hypoalbuminemia was found in each of group 1, 3 and 4. The incorporation of 15N into plasma albumin was higher in group 1, 3 and 4, compared to group 2, which showed a significant decrease in body weight and plasma albumin level. The incorporation of 15N into urea, however, was higher in group 3 and 4, than that of group 1 and 2. The results suggested that: (1) In the rats with liver damage induced by dimethylnitrosamine, synthesis of amino acid in the liver is impaired, although the rate of albumin synthesis from amino acid is still maintained. (2) Parenteral use of amino acid mixture is useful for the maintenance of normal protein synthesis in rats fed with protein deficient diet.