The present study was undertaken in rats to clarify whether endotoxin hepatotoxicity can be modified by phagocytic activity of the reticuloendothelial system. Pretreatment with cortisone acetate, diethylstilbestrol, methyl palmitate, triolein or gadolinium chloride markedly improved the mortality rate from endotoxemia and prevented the development of focal random coagulative hepatocellular necrosis and the elevation of serum transaminase activities due to endotoxemia. Cortisone acetate, methyl palmitate and gadolinium chloride are the well-known depressors of reticuloendothelial phagocytic activity: Diethylstilbestrol and triolein are the stimulators. This suggests that phagocytic activity of the reticuloendothelial system does not relate to not only the mortality rate but also the degree of hepatic injury following endotoxemia.