We have previously observed that glycyrrhizin(GL) inhibits the proliferation of transplanted-L1210 cells via the production of nitric oxide from peritoneal macrophages. In the present study, we examined the effect of GL on Iymphocytes subpopulation change of L1210 cells-transplanted mice. GL increased the population of $CD4^-CD8^+$ cells of thymocytes in L1210 cells-transplanted mice and the lucigenin chemiluminescence of human polymorphonuclear cells. These results suggest that the proliferation of transplanted-L1210 cells is partly inhibited by an enhancement of cytotoxic T cells population and phagocytic activity in GL-administered mice.