As in many other fields of research in biology, the technology of expressing cloned genes in eukaryotic cells has become an increasingly important method for the study of adrenergic receptors (ARs). As developed in Chapter 14, substantial expression of adrenergic receptors can be achieved using different host organisms, including bacteria and yeast. Expression in higher eukaryotic cells is, however, of particular interest because these cells: (1) possess the machinery for proper processing, delivery, and insertion of the recombinant receptors into the membrane; and (2) generally express the GTP binding proteins and the other effector proteins responsible for propagation and amplification of the signal triggered by receptor agonists.