Significant increase of liver succinic dehydrogenase (SHD) activity was produced by carrageenin-induced edema in rats. Pretreatment with human placental extract "Placentrex" inhibited the increased liver SHD activity in a dose-dependent manner. "Placentrex" was found to have no effect on the liver SHD activity in normal rats. Furthermore, heat-induced erythrocyte lysis was inhibited to a substantial extent by "Placentrex" and was found to be almost dose-responsive. However, adenosine diphosphate (ADP)-induced platelet aggregation and trypsin activity were not changed in vitro by the "Placentrex". No alkaline phosphatase activity was found in this preparation. All these studies indicate that the membrane stabilization and depletion of adenosine triphosphate (ATP) synthesis may be the basis of anti-inflammatory effect of this drug.