A case is presented of a patient with the Zollinger-Ellison syndrome who demonstrated unusually high basal pancreatic secretion of fluid and bicarbonate equivalent to mean secretory values in a group of control subjects during maximum secretin stimulation. Following exogenous stimulation with secretin, the patient demonstrated a 2-fold increase in the output of fluid and bicarbonate to values approximately double those reported for normal subjects. The pancreatic capacity for bicarbonate secretion matched the gastric secretory capacity for hydrogen ion. Release of endogenous secretin is thought to be responsible for the high level of basal pancreatic secretion. A functional hypertrophy of the exocrine pancreas is suggested to explain the hypersecretion of fluid and bicarbonate following stimulation with exogenous secretin and the absence of clinically apparent malabsorption in our patient.