In 34 patients the diameter of Wirsung's duct was measured by real-time sonography before and after intravenous application of secretin. 25 of these patients, meeting special criteria, were chosen as normal controls; 9 patients had chronic pancreatitis. Normal subjects with an average duct diameter of 1.8 mm showed an average dilatation by about 89% to a mean value of 3.4 mm, mostly within five minutes. No dilatation was seen in patients with chronic pancreatitis (average duct diameter 2.9 mm), with the exception of one patient. The authors discuss the possibility of assessing pancreatic function and of detecting the presence of a rigid duct in a fibrotic pancreas by sonography. This confirms the usefulness of the sonographic secretin test as a reliable aid in the diagnosis of chronic pancreatitis.