Cholesterol gallstone disease and obesity are common and often associated disorders that could be affected by dysfunction of the receptor for cholecystokinin (CCK). Extending earlier studies that identified a defect at the level of receptor-G protein coupling in cholesterol gallstone disease, we characterized the primary structure of the gallbladder CCK receptor in patients undergoing a cholecystectomy. Represented were patients with cholesterol gallstones, as well as controls with pigment gallstones or without gallbladder disease. Both groups were composed of the range of body habitus from lean to morbidly obese. No evidence of any sequence mutation or polymorphism in the CCK receptor gene was found in any patient. This should lead future investigations of the pathogenesis of these problems toward the possible contribution of the plasmalemmal environment in affecting the association between normal receptors and G proteins.