Background: In the management of acute pancreatitis, oral feeding is prohibited and either enteral or parenteral feeding is commenced for the patients in an effort to not increase the secretion of the pancreatic enzymes. Purpose: This study was undertaken in an attempt to determine the impact of oral feeding on the severity of acute pancreatitis and to compare this impact with that of parenteral feeding. Materials and methods: Twenty-four female Sprague-Dawley rats were divided into two groups. In both groups, acute pancreatitis was induced by ligation of the main biliopancreatic duct. The rats in group I were fed orally and the rats in group II were fed parenterally. The rats were sacrificed at 48 hours, and blood samples were obtained from the heart upon exposure of the abdominal and thoracic cavities. The pancreas and the left lung were removed for histopathological examination. The levels of lactic dehydrogenase (LDH), serum glutamic oxaloacetic transaminase (SGOT), glucose, calcium and blood urea nitrogen, base deficit, partial oxygen pressure, leukocyte count, and hematocrit level among Ranson criteria and the level of amylase were measured. The pancreas and the lung were examined under a light microscope. Results: The levels of LDH, SGOT, and calcium for the rats in group I were significantly higher when compared with the rats in group II (P <0.05). Similarly, the levels of amylase for the rats in group I were found to be higher when compared with the rats in group II, but the difference was not significant. Inflammatory changes observed in the pancreas were less severe whereas inflammatory changes observed in the lung were more severe for the rats in group I when compared with the rats in group II. Conclusion: The blood levels of the enzymes were adversely affected for the rats fed orally. In contrast, inflammatory changes observed in the pancreas were more severe for the rats fed parenterally. The study suggests that certain hormones released from the duodenum upon stimulation by oral nutrient intake lessens the severity of pancreatitis through protective effects on the pancreas, whereas the elevated levels of the enzymes cause endothelial damage resulting in destruction in distant organs such as the lung. Copyright (C) 1999 Excerpta Medica Inc.