Endothelin-1 (ET-1) is a 21 amino acid peptide, first isolated in 1988 from porcine aortic endothelial cells in tissue culture (Figure 1). The peptide was shown to be the most potent known vasoconstrictor of porcine coronary arteries. A powerful endothelium-derived vasoconstrictor had been predicted for some time, but it was when Yanagisawa and his colleagues elucidated the structure, and provided information about the molecular biology and mode of action of the peptide that an unprecedented interest was stimulated in the endothelins.