Gut hormone receptors can be over-expressed in several human cancers and represent the basis for receptortargeted tumor imaging and therapy. A promising receptor for such clinical applications is the cholecystokinin receptor. Cholecystokinin receptors are expressed in numerous neuroendocrine tumors, in particular medullary thyroid carcinomas and neuroendocrine gut tumors, as well as in stromal tumors. Moreover, several radiolabeled CCK or gastrin analogs have been developed allowing to detect these tumors and their metastases in patients using in vivo cholecystokinin receptor scintigraphy, proving the feasibility of targeting CCK receptors in human tumors in vivo.