Complexes of granulocyte elastase and ₁-antitrypsin are markers for granulocyte activation. In 75 patients with acute pancreatitis these complexes were immunologically determined daily in plasma during the first week of hospitalization. Patients were classified into three groups: mild pancreatitis (I, 1 complication, N=34), severe pancreatitis (II, 2 complications, N= 29), lethal outcome (III, N=12). Initially, granulocyte elastase (mean±sem) was lower in group I (348±39 g/liter) as compared to groups II (897±183 g/l) and III (799±244 g/liter), P<0.001 for="" i="" vs="" ii="" +="" iii.="" initial="" elastase="" concentrations="">400 g/liter were consistent with a severe or fatal course of the disease but did not distinguish between severe and lethal pancreatitis. In patients with mild or severe disease, mean elastase concentrations decreased continuously during the following days (197±15 g/liter in mild cases, 325±30 g/liter in severe cases at day 7). In patients with lethal disease, however, mean elastase concentrations even increased at day 2 and remained higher than 700 g/liter during the observation period. At days 1 and 2 the predictive value for severe or lethal disease of raised (>400 g/liter) elastase concentrations [positive predictive value (PPV) 82%, negative predictive value (NPV) 81%] was better than that of elevated (>100 mg/liter) C-reactive protein (PPV 73%, NPV 73%), elevated (>4.0 g/liter) ₁-antitrypsin (PPV 59%, NPV 50%), or decreased (<1.5 g/liter)="">₂-macroglobulin (PPV 82%, NPV 67%). When the time course of the concentrations of the acute-phase proteins was studied, it was found that rises of granulocyte elastase were followed by elevated C-reactive protein levels after one day, by elevated ₁-antitrypsin levels after two days and by decreased ₂-macroglobulin levels after three to four days. We conclude that granulocyte elastase is a good early marker for the severity of acute pancreatitis. Compared with elevated levels of C-reactive protein and ₁-antitrypsin release of granulocyte elastase reflects an event that precedes acute-phase protein induction.