Acute pancreatitis was induced in pigs by manual retrograde injection of Na-taurocholate into the pancreatic duct. Chromogenic peptide substrate assays showed increased trypsin (TRY) and plasma kallikrein activities (KK), parallel with a reduction of prekallikrein (PKK) levels and functional plasma kallikrein inhibition (KKI), in the peritoneal exudate in untreated animals. Pretreatment with C1 inhibitor (C1 INH) concentrate significantly increased the KKI capacity, parallel with unchanged KK and TRY activities in the peritoneal exudate. Furthermore, C1 INH pretreatment significantly improved the hemodynamic performance and the survival rate during a 6-h observation period. The study underlines the pathophysiological importance of trypsin and the plasma kallikrein-kinin system during acute pancreatitis. C1 INH concentrates given intravenously prevent activation of this system locally in the peritoneal exudate during experimental acute pancreatitis.