Mutations in the human serine protease 1 gene (PRSS1), which encodes cationic trypsinogen, can accelerate its autoactivation and cause hereditary or sporadic chronic pancreatitis. Disruption of the locus that encodes cationic trypsinogen in mice (T7) causes loss of expression of the protein, but only partially decreases the severity of secretagogue-induced acute pancreatitis and has no effect on chronic pancreatitis. We investigated whether trypsinogen becomes pathogenic only when it is activated by mutation