In our previous study, we reported that monocyte-activation inhibitory factor was produced by stimulated fibroblasts. We also previously found that glycyrrhizin (GL) had an ability to affect fibroblasts because the proliferation of human fibroblasts was increased by GL. In this study, we demonstrated that culture supernatants from the GL-stimulated fibroblasts inhibited the activation of normal human peripheral monocytes in vitro. Then, studies were performed to know whether GL affects fibroblasts to suppress the granuloma formation. Pulmonary granulomas were induced in guinea pigs by Sephadex beads. The formation of granulomas was significantly suppressed by intraperitoneal injections of GL. Thus, GL was shown to have antigranulomatous effects in vivo.