The pancreatic exocrine secretory response to increasing doses of exogenous caerulein with and without a background infusion of secretin was studied in 5 healthy volunteers. Caerulein over a full range of doses (2.3-37 pmol/kg/h) produced increasing enzyme secretion up to 18.5 pmol/kg/h, whereas 37 pmol/kg/h was clearly supramaximal and caused submaximal enzyme release. We conclude that maximal pancreatic enzyme secretion is achieved with lower caerulein doses than generally used in pancreatic function tests.