The ETB receptor has been found to be predominantly expressed in the vascular endothelium of various bovine tissues by immunostaining with a highly specific antiserum that does not cross-react with ETA. The tissues examined include the lung, trachea, kidney, adrenal gland, pituitary gland, and cerebellum. The wide-spread localization of ETB in the endothelial lining suggests that there is an ETB-mediated autocrine system of endothelin, which plays an important role in regulation of the functions of endothelial cells.