The purpose of this study was to determine the contribution of endotoxin (ET) in ocurrence and progression of acute pancreatitis (AP). The results indicated that correlation of ET changes with multiple organ damage in AP. The degree of ET elevation correlated well with the severty of AP. The level of plasma ET of severe AP patients was much higher than that of mild AP patients (Ｐ＜0.05). The chance of multiple organ damage got greater while the plasma ET level got higher. Moreover, the severety change of severe AP correlated with the change of plasma ET level. In other words, the ET level was reduced while the disease was recovering, elevated while it was becoming worse and maintained high level in dead cases. We think that plasma ET level can be used as a reference for differenciating mild AP with severe AP and a predictor for the prognosis of AP.