The effect of bunolol on ?-adrenergic receptor of various tissues of animals were reported. The results showed that cumulative dose-response curves of isoprenaline were shifted paratlely to the right by bunolol ( 10-8, 10-7, 10-6mol/L ) on isolated rabbit atrium and guinea pig trachea preparation utilizing isoprenaline as a beta-receptor agonist. In the isolated rabbit right atrium preparation,the pA2 value of bunolol antagonizing the chronotropic action of isoprenaline was 9.3. In the isolated guinea-pig trachea preparation,the pA2 value of bunolol antagonizing the isoprenaline-induced relaxation was 9.1. By contrast, the 〔pA2 ( ?1 )- pA2 ( ?2 ) 〕 value of bunolol was 0.2, suggesting its ?-blocking action in the atrium being nearly 0,6 times more than that in the trachea. Also, comparison with pfopranolol, the blocking effect of bunolol on cardiac ?1 receptor and on trachea ?2 receptor were 4 times and 1.6 times more than that of propranolol respectively.Bunolol ( 1 mg/kg ) could, block completely the vasodilating response of epinephrine ( 10?gAg ) . At the same dosage, bunolol had no effect on blood pressure and heart rate of prior reserpini-sation rats.