This study describes a rapid in vitro assay for the order of potency of bronchodilator drugs using specific binding of (−)-[3H] dihydroalprenolol ([3H]DHA) to rat lung membranes. Under linear conditions with respect to tissue, specific binding of [3H]DHA showed saturability, rapid kinetics of association and dissociation of radioligand, and sterospecificity. Nanomolar (nM) concentrations for 50% inhibition (IC50±SE) for the bronchodilator drugs examined were as follows: albuterol, 1485±170; isoproterenol, 136±53; procaterol, 162±28; terbutaline, 3310±934; and zinterol, 51±8.3. A comparison of binding studies using rat lung tissue membranes and similar preparations of rat heart and skeletal muscle demonstrated that lung tissue had 7 to 8 times more receptor sites (Bmax) for [3H]DHA than heart or skeletal muscle. Adenyl cyclase activit of the rat lung membrane preparation almost doubled in the presence of (−)-isoproterenol. Displacement of specific (3H)DHA binding in membrane preparations may provide useful data for evaluating bronchodilator compounds.