Isoproterenol and other agonists readily dissociate from the beta-adrenergic receptor in turkey erythrocyte membranes. However, when a low concentration of deoxycholate is added, the receptor locks the prebound agonist; i.e., the rate of dissociation of the prebound agonist decreases drastically. The dissociation of prebound antagonists is slightly increased by deoxycholate. Locking, which is thus agonist specific, occurs in the cold, is reversed when detergent is removed from the membranes, and appears not to require the guanyl nucleotide binding protein of the adenylate cyclase system. It is suggested that this induced fit of a receptor to an agonist represents the specific conformational response that normally propagates in the receptor molecule in its interaction with the next component along the pathway of signal transmission.