In a prospective evaluation of patients suspected of having chronic pancreatitis, synthesis of pancreatic enzymes was measured by means of the incorporation of selenium-75-labelled methionine into the proteins of duodenal aspirate during stimulation of pancreatic secretion with secretin (1 CU X kg-1 X h-1) plus cholecystokinin (CCK) (1 IDU X kg-1 X h-1). The rate of pancreatic enzyme synthesis was increased in patients with chronic pancreatitis. Measurement of pancreatic enzyme synthesis was more sensitive in the detection of chronic pancreatitis than either the bicarbonate or the trypsin secretory response to secretin plus CCK. A combination of the bicarbonate secretory response with measurement of the rate of enzyme synthesis provided a positive predictive power of 100% when both tests were abnormal and a negative predictive power of 100% when both tests were normal, so that the combined test can be recommended both for excluding and confirming the presence of chronic pancreatitis.