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We have applied a new method for quantitative measurement of bronchial beta adrenoceptor blockade to a new beta adrenoceptor antagonist, bevantolol. Dose-response curves to a beta agonist, albuterol, were obtained in six normal subjects by measuring specific airway conductance (sGaw) after increasing doses of inhaled albuterol. These were repeated on three separate occasions 2 hr after subjects had taken oral placebo or bevantolol (75 or 150 mg), double-blind in random order. The dose-response curves after bevantolol 75 mg were displaced in the right of placebo in four subjects and after 150 mg were displaced to the right of placebo in all subjects. The mean dose ratios for bevantolol 75 or 150 mg were 1.02 and 2.77, much the same as those obtained in the same subjects after practolol 100 and 200 mg and considerably less than that after propranolol 40 mg. The mean reductions in exercise heart rate were 25% and 29% after bevantolol 75 and 150 mg. Our data show that bronchial beta blockade after a beta blocking drug can be assessed quantitatively in many by a double-blind technique.