Peripheral signals from stomach and small intestine are believed to induce satiation. In experimental animals, satiation factors can be transfused pointing to the humoral nature of the signal. Cholecystokinin (CCK) may be an important mediator, since infusion of exogenous CCK has been demonstrated to induce satiation and to inhibit gastric emptying. However, whether this effect of CCK is a physiological or pharmacological event is a matter of controversy. The significance of exogenous CCK or stimulation of endogenous CCK in the possible treatment of obesity requires further study.