Protease activated receptor-2 (PAR-2) is present in the pancreas, where it has been shown to play a protective role during pancreatitis. However, the mechanism by which it protects still remains to be elucidated. Acute pancreatitis is associated with premature zymogen activation and a blockage in digestive enzyme secretion. In this study, we have examined the effects of PAR-2 activation on the severity of pancreatitis to determine if its protective effects are mediated by affecting either or both premature activation and secretory blockage. Our results confirmed that PAR-2 -/- mice have more severe pancreatitis compared to wild type mice. Interestingly, intrapancreatic trypsin levels in the PAR- 2 knockouts remained elevated after 6 hours of pancreatitis, while they reverted to normal in the wild types. During pancreatitis, PAR-2 mRNA levels were upregulated in wild type mice in response to supramaximal caerulein administration. Further, following a single injection of supramaximal caerulein, PAR-2 mRNA levels were also elevated, reaching a peak at 3 hours. Stimulating PAR-2 with trypsin or the PAR-2 activating peptide, SLIGRL, induced significantly more secretion from the acini of these caerulein-sensitized mice compared with the controls. PAR-2 activation also reversed the inhibition of secretion observed in both the caerulein and arginine models. Based on our findings, we hypothesize that trypsin released during the early stages of pancreatitis activates PAR-2 receptors on the acinar cells and stimulates secretion from these cells. Thus PAR-2 activation may reduce pancreatic injury and limit the severity of pancreatitis by allowing extracellular trypsin to act as a secretagogue.