To study the dynamics of pathomorphologic alterations in the development of acute pancreatitis (AP) and the corresponding changes of the patterns of pancreatic enzymes in rats AP was induced by: 1) combination of a pancreatic juice edema and temporary pancreatic ischemia, ii) by intraductal instillation of trypsin, and iii) by trypsin instillation in combination with ischemia. At 4, 8 and 24 h postoperatively the histologic findings and the activities of lipase and alpha-amylase in the pancreas and the serum were analyzed. The histologic sum score of the individual rats did not correlate with their enzymic patterns in pancreas and in serum. In all three models there was a development of parenchymal necrosis independent of the existence of pancreatic fat necrosis. Therefore, it is not probable that fat necrosis represents an obligatory precondition for the initiation of autodigestion.