The elastase levels in rat serum were measured in experimental pancreatic disorders by radioimmunoassay. After the induction of acute pancreatitis either by trypsin or normal saline, the serum elastase levels increased significantly. The serum elastase levels in trypsin induced pancreatitis were significantly higher than in normal saline induced pancreatitis. The levels in ascitic fluid were also higher in trypsin induced pancreatitis than in normal saline induced pancreatitis. Microscopically, haemorrhagic pancreatitis was found in trypsin induced pancreatitis and edemotous pancreatitis was found in normal saline induced pancreatitis. The serum elastase levels decreased significantly in rats who were treated by ethionine for long period. Microscopically, atrophic pancreas was found in those rats. These results suggest that the measurement of pancreatic elastase in either blood or ascitic fluid by radioimmunoassay is a useful diagnostic method for pancreatic disorders, especially in acute pancreatitis.