This assay employs the competitive inhibition enzyme immunoassay technique. A monoclonal antibody specific to Endothelin 1 (EDN1) has been pre-coated onto a microplate. A competitive inhibition reaction is launched between biotin labeled Endothelin 1 (EDN1) and unlabeled Endothelin 1 (EDN1) (Standards or samples) with the pre-coated antibody specific to Endothelin 1 (EDN1). After incubation the unbound conjugate is washed off. Next, avidin conjugated to Horseradish Peroxidase (HRP) is added to e