ELEVATED serum amylase activity in a patient with abdominal pain usually indicates pancreatitis. Ordinarily, the amylase level returns to normal within several days; however, a small percentage of subjects manifest more persistent hyperamylasemia. Although continued activity of pancreatitis, a pseudocyst, or pancreatic ascites accounts for some of these cases of persistent hyperamylasemia, in many subjects diagnostic evaluation fails to reveal pancreatic disease. This report, which describes the isoamylase finding in 28 patients with chronic hyperamylasemia, indicates that the pancreas is seldom responsible for persistent, unexplained elevations of serum amylase activity. Subjects and Methods Isoamylase studies were carried out in serums. . .