Objective: To study if the immune-enhancing effect of Arg was mediated via liver.Methods: The direct effect of Arg on T cell proliferation was measured by 3H-TdR incorporation. Rat hepatocytes were primarily cultured in serum-free DMEM/F12 medium, and then cultured in medium containing Arg(?mol/L:0,7.5,75,750,7 500), and the supernatant was collected at 0, 24, 48, 72 hours, and added to splenocytes culture, and T cell proliferation, NK cell activity and IL-2 activity,〔Ca 2+〕i were measured respectively.Results: Arg had no direct effect on splenocyte proliferation. The hepatocyte culture supernatant significantly increased the lymphocyte〔Ca 2+〕i ,IL-2 activity and T lymphocyte proliferation; 7 500 ?mol/L was most effective. Conclusion: Arg may enhance immune function via secretion of bioactive molecules by hepatocytes.