Serum elastase 1 has been evaluated in 115 patients with pancreatic and nonpancreatic gastrointestinal diseases and in 36 healthy controls. Increased serum elastase 1 values were found in all 27 patients with acute pancreatitis. If the diagnostic cutoff was established as the 2-fold increase above the upper normal range, sensitivity of elastase 1 (100%) was superior to pancreatic lipase (90%), immunoreactive trypsin (87%) and pancreatic amylase (78%). Specificity was 96% for elastase 1 at this cutoff. No distinction was possible between edematous and necrotizing acute pancreatitis on the basis of peak serum elastase 1 concentrations. Among 32 patients with chronic pancreatitis increased serum elastase 1 values were found in 22% and decreased values in 16% of patients, showing a striking parallelism to serum values of pancreatic lipase and immunoreactive trypsin. Specificity, established in controls and 49 patients with different gastrointestinal diseases, was 77% for elastase 1, 76% for immunoreactive trypsin, 83% for pancreatic lipase and 91% for pancreatic amylase. In addition, we investigated 21 patients with severe chronic renal diseases. In patients with renal insufficiency elastase was increased in 33%, comparable to the frequency of increased amylase and pancreatic amylase serum levels, whereas immunoreactive trypsin was increased in 95%. Immunoreactive trypsin showed a significant correlation to creatinin serum concentration, whereas the other enzymes did not.