A method for screening an antagonist of the human endothelin receptor so as to identify and study agents of the circulatory system, comprising the steps of contacting a sample comprising a protein receptor with a candidate compound, the protein receptor having high affinity for human ET-1 and ET-2 and lower affinity for human ET-3 and an amino acid sequence from Asp at +1 to Asn at + 407 as shown in SEQ ID NO: 1, and detecting the binding of the candidate compound to the protein receptor. The agent of the circulatory system can used in the manufacture of medicament for treatment of essential hypertension, vasospastic stenocardia, acute myocardial infarction, chronic renal insufficiency, subarachnoid hemorrhage and hypoxia.