Growth hormone-releasing factors (GRF's) from two human pancreatic tumors (hpGRF's) that caused acromegaly and from the rat hypothalamus ( rhGRF ) were recently isolated and characterized. Although these peptides are potent growth hormone secretagogues, they have not until now been described to have actions outside the pituitary. These GRF's were shown to stimulate digestive enzyme secretion from an exocrine pancreatic preparation in vitro, rhGRF being more than 100 times as potent as hpGRF. Adenosine 3',5'-monophosphate mediates this action of the GRF's.