RP-72540 is a cholecystokinin B receptor antagonist. RP 72540 showed selectivity factors in express of 200 for CCKA versus CCKB receptors and also had high affinity for gastrin binding sites in the stomach. Administration of RP-72540 resulted in a dose-dependent inhibition of [3H]pCCK-8 binding in mouse brain homogenate. However, the relative penetration of RP-72540 into the forebrain after peripheral administration was below 0.01%.