In 27 beagle dogs, acute necrotizing pancreatitis was induced by retrograde injection of autologous bile and trypsin into the main pancreatic duct. Animals were randomly assigned to the following treatments: group 1--(9 dogs) aprotinin 600,000 KIU/d by i.v. route; group 2--(9 dogs) peritoneal dialysis for 6 d plus 500,000 KIU/L of aprotinin in the dialysate fluid; group 3--(9 dogs) peritoneal dialysis without aprotinin in the dialysate fluid. All dogs of the group 1 died within 16 h following the induction of pancreatitis and extensive necrotizing and hemorrhagic changes were seen in the pancreatic and peripancreatic areas. Six dogs of the group 2 survived and no necrotizing changes were observed 30 or 50 d after the induction of pancreatitis. Three dogs of the group 3 survived, but slight necrotizing lesions were found at the autopsy. The survival rate was higher in dogs with peritoneal lavage (p = 0.0129) or with peritoneal lavage plus aprotinin (p less than 0.0001) than in those receiving i.v. aprotinin, indicating that the latter treatment has no beneficiary effect on the course of acute pancreatitis.