A model of acute pancreatitis (AP) was developed by application of anti-acinar-cell-antiserum in rats. Within 24 h postoperatively the binding of antibodies to the pancreas, histological findings, and the activities of lipase and a-amylase in serum and pancreas were analyzed. While after intraaortic administration morphological alterations could not be observed, after single dose intraductal injection, typical macroscopical and histological signs of AP were found. This pancreatic injury was characterized by a mild and protracted course favoring investigations of the early phase of pathogenesis. As soon as 2 h after intraductal application of antiserum, serum amylase and lipase were already increased and microscopic examination of the pancreatic tissue revealed pancreatic edema, inflammatory infiltration and parenchymal necrosis. Intra- and extrapancreatic fat necrosis occurred at 16 h post injectionem. The results suggest that parenchymal damage plays an essential role in the manifestation of this experimental AP and that fat necrosis seems to be a secondary event.