['Acute pancreatitis is a common complication after endoscopic sphincterotomy (ES) and endoscopic retrograde cholangiopancreatography (ERCP). The aim of this study was to detect the time when the peak of serum amylase was predictive for pancreatitis or severe hyperamylasemia, to plan a prolonged follow-up in the hospital and for outpatients.', 'In a prospective series of 409 consecutive patients undergoing ES, serum amylase activity was measured immediately before the procedure and 2, 4, 8, and 24 h thereafter; the data obtained at 2, 4, and 8 h were compared with those at 24 h and with the outcome. Sensitivity for long-lasting severe hyperamylasemia (more than five times the upper normal limit) and pancreatitis were also defined for all sampling times.', 'At 24 h after ES, amylase was still more than five times the upper normal limit in 26 patients, 19 of whom had mild/moderate acute pancreatitis. There was a significant difference (p < 0.01 at all sampling times) between the 26 patients with 24-h severe hyperamylasemia and those with lower levels. The sensitivity of amylase measurement in detecting pancreatitis or long-lasting severe hyperamylasemia was highest at 8 h. However, the 4-h assessment appears to be a reliable predictor in practice, as more than two-thirds of cases of pancreatitis (all but one with computed tomography-confirmed pancreatitis) occurred among patients whose 4-h amylasemia was higher than five times the upper normal limit.'] Is serum amylase measured four hours after endoscopic sphincterotomy a reliable predictor of postprocedure pancreatitis?