GOSEKI, N., ENDO, M., ONODERA, T. and KOSAKI, G. Influence of L-Methionine-Deprived Total Parenteral Nutrition on the Tumor Tissue and Plasma Amino Acids Fraction and the Host Metabolism: Experimental Study with Sato Lung Carcinoma-Bearing Rats. Tohoku J. Exp. Med., 1989, 157 (3), 251-260-Creation of an amino acid imbalance, particularly curtailment of L-methionine, at the tumor cell level is thought to have a favorable effect on the inhibition of tumor growth. In the present study, we examined the influence of a specially-formulated amino acid mixture, avoid of sulfur-containing amino acids (L-methionine and L-cysteine), on the growth and amino acid fraction of Sato lung carcinoma (SLC) and the host metabolism in SLC-bearing rats. The rats were treated by total parenteral nutrition containing the above amino acid mixture, plus other nutrients (methionine-deprived TPN) for 10 days. Tumor growth began to decrease 4 days after the start of this treatment and the size was significantly less at the end of the treatment than in rats receiving conventional TPN with general purpose Vuj-N type amino acid solution as a protein source. The tumor-to-carcass weight ratio also showed a similar trend. In biochemistry, the albumin level and albumin-to- globulin ratio were significantly lower than in the rats receiving conventional TPN but other parameters such as total protein, glucose, GOT and GPT were not affected by the treatment. In the amino acid fraction of the tumor tissue extraction, both L-methionine and L-tyrosine were decreased and L-serine was increased significantly compared with the control group.