The combination of immunological advances with membrane receptor research has promoted rapid progress in the molecular characterization of neurotransmitter receptor molecules. We have to date produced monoclonal antibodies to beta 1-, beta 2-, and alpha 1-adrenergic, D2-dopaminergic, and muscarinic receptors. In addition we have discovered that some allergic respiratory disease patients possess circulating autoantibodies to beta 2-adrenergic receptors. These antireceptor antibodies in conjunction with specific receptor affinity reagents have allowed us to isolate, purify, and begin to characterize alpha- and beta-adrenergic, dopaminergic, and muscarinic receptors. For example, immunoprecipitation of turkey erythrocyte beta 1 receptors with monoclonal antibodies yields a single polypeptide Mr 65--70 K. In contrast, purification of beta 2-adrenergic receptors using either autoantibodies or monoclonal antibodies yields a receptor species with a subunit of Mr 55--59 K. Autoantibodies to beta 2 receptors demonstrate a 50--100% homology among beta 2 receptors from humans to rats, whereas monoclonal antibody FV-104 recognizes a determinant in the ligand binding site of all beta 1 and beta 2 receptors tested to date. These data suggest that beta 1- and beta 2-adrenergic receptors may have evolved from a common ancestor, perhaps by gene duplication.