In medical practice, diagnostic and therapeutic aspects of gastrointestinal hormones attract interest. Gastrin--in the form of pentagastrin--can be used for gastric secretory analysis and, in the analysis of exocrine pancreatic function, secretin and cholecystokinin-pancreozymin can be employed as stimulants. Diagnosis of hormone-producing tumors is possible by radioimmunological determination of serum levels of the hormone in question: so, dramatically high gastrin levels can be found in the Zollinger-Ellison syndrome while in the Verner-Morrison syndrome, VIP (vasoactive intestinal peptide) values are significantly elevated.--The therapeutic use of gastrointestinal hormones (gastrin, secretin) is waiting in the wings.