In patients suffering from acute pancreatitis, the pathogenesis is not completely understood, and several recent studies in vitro suggested that heat shock proteins might play an important role in cell signaling. To investigate the possible role of extracellular heat shock protein 70 (Hsp70) in pancreatitis, toll-like receptor-4 (TLR4)-deficient and wild-type mice were administered with exogenous Hsp70 during the course of cerulein-induced pancreatitis (CIP). Acute pancreatitis was induced by 5 intraperitoneal injections of cerulein at hourly intervals, and then treated with recombinant Hsp70 through the caudal vein 4 hours after the start of cerulein injections. Subsequently serum amylase and serum cytokines levels were detected. Histologic alteration of the pancreas was evaluated. Tumor necrosis factor alpha (TNF-alpha) concentrations and myeloperoxidase (MPO) activity in both pancreas and lungs were analyzed. The nuclear factor kappa B (NF-kappaB) activation in pancreatic tissue was measured using a sensitive RelA enzyme-linked immunosorbent assay. Treatment with recombinant Hsp70 to wild-type mice in CIP resulted in significant aggravation of inflammation in pancreas, elevated levels of serum cytokines, up-regulation of pulmonary MPO activity and increase of lung tissues TNF-alpha concentrations. In contrast, treatment with Hsp70 to TLR4-deficient mice had little effect on serum cytokines levels, pancreatic inflammation, pulmonary MPO activity and TNF-alpha concentrations. The results suggest that extracellular Hsp70 might induce systemic inflammatory response syndrome (SIRS)-like response in vivo and TLR4 might be involved in the Hsp70-mediated activation of inflammatory reaction in the progression of CIP without infection.