The metabolic effects of total parenteral nutrition (TPN) solutions containing different profiles of individual amino acids were investigated in the rats bearing Walker 256 carcinosarcoma. The rats were subcutaneously inoculated with 10(7) tumor cells and 6 days later were continuously infused intravenously for 8 days with three different TPN solutions. The experimental and control solutions were composed of high concentrations of branched chain amino acids (BCAA) and arginine (high Arg + BCAA TPN), high concentrations of BCAA (high BCAA TPN) and regular amino acids (regular TPN), respectively, and were isonitrogenous, isocaloric, and isovolemic. Rats receiving subcutaneous injection of saline rather than tumor cells received high Arg + BCAA TPN as pair-fed controls. The flooding dose method of 14C-leucine was used for the analysis of protein synthesis. With the feeding of high Arg + BCAA TPN, the tumor-bearing rats revealed a smaller increase of tumor volume and lower tumor fractional rates of growth (Kg) and synthesis (Ks) as well as protein synthesis (PS), compared with the high BCAA TPN and regular TPN in tumor-bearing rats. There were no significant differences of Ks and PS in liver and muscle between TPN groups, whereas tumor-bearing rats infused with high Arg + BCAA TPN displayed higher levels of whole-body Ks and PS than other TPN groups in tumor-bearing rats and pair-fed nontumorous rats. Except for liver RNA content which showed a lower level in tumor-bearing rats with high Arg + BCAA TPN, no other differences of DNA and RNA contents were found in tumor, liver, and muscle of the different TPN groups. The current results indicate that individual amino acids can influence tumor growth and protein metabolism, and that arginine, in combination with BCAA, may reduce tumor growth through a reduction in protein synthesis.