The protective effect of human urinary trypsin inhibitor (UTI) on acute pancreatitis was studied in beagle model. After pancreatitis was experimentally induced in beagle dogs by infusing trypsin and sodium taurocholate into the accessory pancreatic ducts under laprotomy, effects of UTI were compared to those of aprotinin. Routine physical examination, hematology and blood chemistry values were used as parameters and checked on a periodical basis during the experiment. At the end of experiment, surviving animals were sacrificed and liver, kidney, and pancreas were histologically examined. The results of this study warrant the development of UTI as new therapeutics for acute pancreatitis.