The cholecystokinin (CCK) family of peptide hormones have been implicated in numerous important physiologic events. These appear to be mediated through 2 general classes of receptors, A (CCKAR)and B (CCKBR), based on their binding affinities for CCK/gastrin family peptides. Through binding to class A receptors, CCK is a major physiologic mediator of gallbladder contraction and pancreatic enzyme secretion. It appears to play a role in slowing gastric emptying, relaxation of the sphincter of Oddi, and potentiation of insulin secretion. Further, it has been implicated as a mediator of pancreatic growth and tumorigenesis. Class A receptors have also been described in the anterior pituitary, myenteric plexus, and regions of the central nervous system, where they have been implicated in the pathogenesis of feeding disorders, Parkinson disease, schizophrenia, and drug addiction.