Remarkably elevated levels of phospholipase A(2) (PLA(2)) are measurable in human blood samples in cases of acute pancreatitis. The source of the enzyme was first thought to be exclusively the pancreas, but now it is generally accepted that two isoenzymes the pancreatic PLA(2), group I, and the extrapancreatic PLA(2), group II contribute to the raised activity. In contrast to the group II-PLA(2), the pancreatic PLA(2) is heatresistant for 1 hour at 60 degreesC. The catalytically inactive proenzyme of the pancreatic PLA(2) can be activated by trypsin. The aim of our study was to evaluate the diagnostic value of PLA(2) isoenzyme activity measurements to identify patients with severe complications in acute pancreatitis. Blood samples from patients suffering from acute pancreatitis were analyzed for catalytically active pancreatic PLA(2) on day 1 and 2 of hospitalization with a modified radiometric Escherichia colibased PLA(2) assay. In 10 of 41 patients clearly elevated values of catalytically active, heatresistant pancreatic PLA(2) (7.2 to 81.2 U/l) were observed. This group of patients was characterized by severe complications (necrotizing pancreatitis, shock, sepsis, respiratory problems) of which two patients subsequently died. Patients with low or undetectable activity (<7 U/l) of pancreatic PLA(2) recovered rapidly. According to these results the presence of catalytically active pancreatic PLA(2) in serum is associated with severe complications of acute pancreatitis. In contrast to total serumPLA(2), the catalytic concentration of pancreatic PLA(2) can serve as a prognostic marker in acute pancreatitis.