THE DIAGNOSIS of acute pancreatitis is a common challenge even to the most alert clinician. Although an increased blood amylase level is a well recognized diagnostic criterion in acute pancreatitis,1 this value frequently falls below diagnostic levels within 48 to 72 hours after the onset of the disease.2 Furthermore, other tests designed for the diagnosis of late acute pancreatitis are less specific3 and too time consuming. Patients seen relatively late in the course of acute pancreatitis who present residual signs and symptoms and a normal blood amylase often present difficult diagnostic problems. Previous observations4 have demonstrated that the peritoneal fluid obtained from these patients at the time of laparotomy has a high amylase value. This finding suggested that a diagnosis in late cases of pancreatitis might be established by an analysis of fluid obtained by paracentesis. The study of the amylase value of fluid obtained by