A closed duodenal loop was created by the obstruction of the duodenum on either side of the common bile duct. Acute hemorrhagic pancreatitis developed within 24 h with interlobular edema, marked acinar cell necrosis, intra-abdominal fat necrosis and ascites. Plasma amylase activity was greatly increased together with a marked decrease in albumin. There was a temporary abnormality of liver function tests due to obstruction of bile. When the duodenal obstruction was released and the animals allowed to survive, there was at 3 wk a marked reduction in the pancreatic acinar cells with fibrosis and areas of necrosis and chronic inflammatory cell infiltration. Plasma amylase activity was normal but there was an increase in total plasma protein at 3 wk. This technique of a closed duodenal loop in the rat gives a simple, reliable and economic experimental model for studies on acute and chronic fibrotic pancreatitis.