Endothelin (ET) was initially identified as a potent vasoconstrictor peptide with 21 amino-acid residues, produced by cultured porcine aortic endothelial cells. Cloning of the ET genes revealed the existence of three isopeptides, ET-1, ET-2 and ET-3, which are widely distributed in a variety of tissues and possess wide variety of pharmacological functions. Recently, two subtypes of ET receptor have been isolated by the expression cloning technique and the molecular characteristics of the receptors were elucidated. Subsequently, the structural organizations of the ET receptor genes have been investigated. This article discusses the structure, function and expression of ET ligands and receptors from the molecular biological aspect.