L- Arginine has great potential as an immunomodulator and may prove useful in catabolic conditions such as severe sepsis and postoperative stress. There is a body of evidence suggesting that supplemental arginine upregulates immune function and reduces the incidence of postoperative infection. More modest improvements in nitrogen balance have been observed. Tumor response to arginine appears to depend on the immunogenicity of the particular tumor and on the requirement of arginine by the tumor as a growth substrate. Of note, ornithine shares the thymotrophic, immuno stimulatory and secretagogue effects of arginine. It is, therefore, likely that these compounds share the same cellular mechanism of action or that arginine acts via increasing the concentration of available ornithine- Nutrition. 1998 Jul-Aug;14(7-8):611-7.