The level of serum pancreatic polypeptide (PP) in response to intravenous Boots secretin has been measured by radioimmunoassay in 50 patients with documented chronic pancreatitis and 33 controls with no evidence of pancreatitis. Both groups showed significant increases in serum PP but patients with chronic pancreatitis had a significantly smaller response than controls. An abnormal PP response to Boots secretin has been defined as a peak/basal ratio of less than five. Using this criterion. 90% of patients with chronic pancreatitis had a ratio of less than 5, whereas 91% of controls had a ratio of 5 or greater. There was a 92% correlation between a normal or abnormal pancreatic bicarbonate concentration and a normal or abnormal peak/basal PP ratio in response to Boots secretin. These results suggest that the serum PP response to Boots secretin may provide a simple, inexpensive and noninvasive method of accurately diagnosing chronic pancreatitis.