The first aim of this study was to observe the early changes of exocrine function and mor- phology after single large dose of irradiation on rat pancreas. In addition, the relationships among irradiated pancreas, hypertrophied pancreas and acute pancreatitis were investigated. Male Sprague Dawley rats were used. Single irradiation was given using linear accelerator with 6 MeV elecrron beam, dose of 2000 cGy. Acute interstit,ial pancreatitis was induced by four subcutaneous injections of caerulein 20pg/kg at every hour. Camostat 200 mg. Kg(I. G.) was administered for four days to induce pancreatic hypertrophy. The pancreas weight(g/ 100g B. W.) was increased after irradiation but tissue protein and amylase content.s were de- creased. The pancreatic juice volume were increased at 3 days and 1 week, and t.hen norma- lized at 3 weeks after irradiation. The pancreatic juice voume, protein and amylase output were decreased in rats with caerulein induced acute pancreatitis. A decrement of the pancre- atic juice volume in acute pancreatit,is was larger in rats with irradiation than in rats without irradiation. Irradiat,ion worsend the morphologic changes associated with caerulein induced pancreatitis, which were markedly noted at I week after irradiation. Camostat induced hypertrophied pancreas exhibited rnore severe morpologic changes in response tho irradiation combined with caerulein.