Cholecystokinin (CCK)-A and CCK-B receptors are highly homologous members of the seven transmembrane domain G-protein-coupled receptor super-family. Peptides in the cholecystokinin (CCK) family have a variety of biological functions in the central and peripheral nervous systems as well as in the gastrointestinal tract. The CCKA receptor has a more limited distribution with the highest densities in the hypothalamic nuclei, areas of the hippocampus, the septum, dorsal motor vagal nucleus, and interpeduncular nucleus of the brain stem. It also occurs in numerous gastro-intestinal tissues. Binding of ligands to CCK1 stimulates mobilization of intracellular calcium by activation of Gq/11. CCKA receptors affect satiety, pancreatitis, and gut motility and have growth-promoting effects on some tumors.