Abstract-The~-adrenergic blocking and hemodynamic properties of 5-(3-tert-butyl amino-2-hydroxy) propoxy-3, 4-dihydrocarbostyril hydrochloride (OPC-1085) were investigated and compared with those of propranolol and pindolol on myocardial contractile force, heart rate and arterial blood pressure in pentobarbital anesthetized dogs. OPC-1085 showed almost the same ~-adrenergic blocking potency as pindolol, but was approximately 30 and 20 times stronger than propranolol against isopro terenol and cardiac nerve stimulation, respectively. Slight negative inotropic and chronotropic responses were observed with OPC-1085 in effective blocking doses from 1 to 10 pg/kg but were converted to positive ones in doses from 30 to 30001ppg/kg in non-reserpinized dogs. In reserpinized dogs, both OPC-1085 and pindolol in duced only positive responses. These responses were more evident with OPC-1085.