Infection of pancreatic necrosis is a severe complication of acute pancreatitis. Because Toll-like receptor 4 (TLR4) has been identified as a receptor necessary to transduct the signal of bacteria-derived lipopolysaccharide into cells, we investigated the role of TLR4 on pancreatic and pulmonary injury in acute pancreatitis and acute pancreatitis associated with endotoxemia in wild-type and TLR4-deficient mice.