These experiments were conducted to investigate effects of glycyrrhizin (GL) on apoptosis of transplanted-L1210 cells in mice. GL induced apoptosis of transplanted-Ll2lO cells. GL increased nitric oxide production from peritoneal macrophages of L1210 cells-transplanted mice. NOC12, nitric oxide donor, induced apoptosis of L1210 cells in vitro. The apoptosis of L1210 cells were enhanced by co-culture of the peritoneal macrophages of GL-administered mice and L1210 cells in vitro, and was inhibited by L-NMMA. These results suggest that the apoptosis of transplanted-Ll2lO cells is partly induced by nitric oxide produced from peritoneal macrophages in GL-administered mice.