A large number of receptors for neurotransmitters and hormones have been identified by pharmacological studies and by molecular cloning. These receptors are divided into homologous families, which consist of a number of even more homologous subtypes. At least nine distinct adrenergic receptor (AR) subtypes have so far been identified, each of which is the product of a separate gene (1), and some of these are known to have additional splice variants (2,3). Studies of these receptor subtypes in tissues where they are endogenously expressed are often complicated by the presence of many different cell types and coexisting receptor subtypes. The use of cell lines that endogenously express known complements of AR subtypes, or are stably transfected with receptor cDNAs, provides valuable tools for studying the pharmacological properties and functional characteristics of individual receptor subtypes (4). Cell lines expressing a single AR subtype can be identified and used to study their signaling properties in the absence of other subtypes. Receptor cDNAs can be heterologously expressed in cells that natively express no AR subtypes, minimizing potential complications and interference from closely related subtypes. Different receptor subtypes can be expressed in the same cell line, allowing direct comparison of their pharmacology and signaling properties in the same cellular phenotype. Using established cell lines expressing receptor cDNAs makes it possible to obtain high levels of receptor expression, facilitating receptor purification.