To better understand the interaction between f3-adrenergic ligands and their specific membrane receptors, we have undertaken to isolate and purify the various components intervening in the catecholamine-mediated activation of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1]. For this purpose we have developed an affinity chromatography method that allows physical separation of the functional cyclase and f3-adrenergic receptors from turkey erythrocyte membranes (1).Various biochemical and pharmacological properties of the receptors were described (2). The minute amounts of protein prepared by this method and the risk of losing essential components of the receptor cyclase complex during the membrane purification and solubilization steps prompted us to develop a second line of investigation based on immunological methods.Anti-receptor antibodies can be obtained by immunization of rabbits and mice with purified ,B-adrenergic receptor, but most of the antibodies react with parts of the molecule other than the binding site (ref. 3; unpublished data). This is in agreement with observations made in other systems: animals do not make anti-receptor binding site antibodies upon immunization with insulin, acetylcholine, or thyrotropin receptors despite the fact that in pathological conditions such as autoimmune diabetes (4), myasthenia gravis (5), Graves disease (6), and 02-adrenergic hyporesponsiveness in allergic rhinitis (7) anti-binding site antibodies probably constitute an important basis for the etiopathogeny.