To assess the usefulness of endoscopic retrograde cholangiography (ERCP) in the study of acute pancreatitis, 101 of a possible 114 patients (89 per cent) with acute pancreatitis underwent ERCP after recovery from acute illness. In 81 per cent, ERCP was performed within two weeks of recovery. The biliary tract was successfully demonstrated in 87 per cent of the patients and the pancreatic duct in 73 per cent. Roentgenograms of the biliary tract showed stones in the gallbladder in 40 per cent of the patients and in 36 per cent in the biliary ducts. In addition, the gallbladder was not visualized in nine patients. In eight of those patients, the gallbladder was subsequently shown to be abnormal. Other findings of the biliary system included one patient each with clonorchiasis, ascariasis and malignant disease. Changes in the pancreatic duct were detected in 11 per cent of the patients. Most of the changes were consistent with acute or chronic pancreatitis. Minimal morbidity was encountered. ERCP is very accurate in identifying the biliary causes of pancreatitis. In areas where a significant proportion of acute pancreatitis has biliary causes, it should be performed upon all patients soon after resolution of the acute illness to identify those patients who will benefit from early operation upon the biliary tract.