The diagnosis of pancreatic disease is difficult. The first step is clinical suspicion, based on the symptoms and signs. If pancreatic disease is suspected, investigation is necessary to prove this diagnosis. Investigation aims to answer two questions: a) is there pancreatic disease and b) if so, what type? The first question may be answered by demonstrating abnormal pancreatic function, using pancreatic function tests, whereas the second is answered by using techniques to demonstrate structural (anatomical) abnormalities of the pancreas. a) The methods to establish abnormal pancreatic function consist of 1. tests to demonstrate abnormal digestive capability, 2. tests to study pancreatic exocrine secretion, and 3. tests to study endocrine secretion. The tests of group 1 are: chemical fat balance study before and during enzyme replacement therapy, faecal nitrogen balance study, and the demonstration of either the malabsorption of vitamins A, D and K or the sequelae of their malabsorption (low serum calcium, high alkaline phosphatase, prolonged prothrombin time, etc.). Abnormal vitamin B12 absorption also may be present. 2. The tests designed to study pancreatic exocrine secretion are determination of the presence or absence of proteolytic enzymes in the stool, the secretion test, the pancreozymin stimulation test and the Lundh test. The serum amylase and lipase values are of little help in assessment of pancreatic function. 3. The tests to study endocrine function are the glucose tolerances test (which frequently gives abnormal results in pancreatic disease), and radioimmunoassays for insulin and gastrointestinal hormones (which may be increased in patients with functioning tumours of the islet cells). b) The techniques used to establish structural abnormalities of the pancreas are: duodenal cytology (during secretin tests), radiological techniques (abdominal survey films, barium meal, hypotonic duodenography, roentgenography of the biliary tract, barium enema, and angiography,) gastroscopy, duodensocopy, endoscopy and retrograde pancreatography, echography, scan and laparotomy. The relative value of these tests is discussed.