Sodium taurocholate injected into the pancreatic duct system of the rat caused acute haemorrhagic pancreatitis. The pancreatic lesions were immediate and characterized by interstitial oedema, extensive necrotic changes of the acinar cells, and haemorrhages during the first 24 h after the injection. In animals surviving 72 h there were marked acinar atrophy and pancreatic fibrosis. The mortality increased according to the amount of sodium taurocholate injected. Except for necrosis of occasional liver cells, other organs examined were histologically normal. This investigation created an experimental model for studying the pathogenesis of acute pancreatitis. The results support the hypothesis that bile can initiate acute haemorrhagic pancreatitis.