Changes were examined in myocardial catecholamine content and α₁- and β₁-adrenoceptors during the development of cardiomyopathy in Syrian hamsters (Bio 14.6) and age-matched healty controls. In addition, the effects of bunazosin, atenolol, xamoterol, ketanserin, and verapamil on the catecholamine content and [³H]prazosin, [³H]CGP12177 bindings to α₁- and β₁-adrenergic receptors of myocardium were compared with those of the controls. (1) Lower norepinephrine and dopamine levels were observed in 35-week-old cardiomyopathic hamster hearts than in the controls. There was, however, a tendency for a slight decrease of α₁- and β₁-adrenoceptors in cardiomyopathic hamsters. (2) Administration of bunazosin induced lower dopamine values in 18-week-old cardiomyopathic hamsters. (3) Xamoterol induced a higher K_d value for β₁-adrenoceptors and lower dopamine content than for those with cardiomyopathy. Ketanserin also induced a higher B_max value than for cardiomyopathy. Thus, drug treatments clearly change catecholamine content and binding characteristics of the adrenoceptors which play an important role in the development of cardiac hypertrophy and heart failure.