Background: The bacterial contamination of pancreatic necrosis in acute pancreatitis is supposed to occur through translocation of intestinal bacteria. Increased gut permeability may be the initial phenomenon in this process. To test the hypothesis that gut permeability is increased in acute pancreatitis a clinical study was made where gut absorption and permeability were assessed with multi-sugar probes in patients with acute pancreatitis within 2 days after admission to hospital and again after recovery of disease. Methods and Results: Twenty-three patients with acute pancreatitis and 20 healthy controls were studied. According to Atlanta classification, 15 patients had mild and 8 patients severe pancreatitis. Gut absorption, assessed as the 5-h urine excretion of L-rhamnose, D-xylose and 3-O-methylglucose, was decreased in patients with acute pancreatitis and more pronounced in patients with severe pancreatitis (L-rhamnose and D-xylose: P < 0.001; 3- O -methylglucose: P