Since the discovery of endothelins, peptides with exceptional vasoconstrictor potency that were originally suggested to act by causing the opening of Ca2+ channels, it has emerged that these agents are important in intercellular communication in many tissues. They exert their effects through G protein-coupled receptors, of which two classes have been cloned. Robert Miller, John Pelton and John Huggins review the progress made towards a molecular understanding of ligand recognition by endothelin receptors. Receptor-selective agonists and antagonists have emerged from attempts to understand the three-dimensional structure of the endothelin pharmacophore, from structure-activity studies and from rapid-screening programmes. From the nature of the secretion and action of endothelins, it would seem that these peptides are involved in long-term changes rather than in acute responses to stimuli, and that they are likely to be important in a number of pathological states. Evidence suggests that receptor antagonists with appropriate affinity and selectivity may be useful in the treatment of conditions as diverse as hypertension, ulcerogenesis and ciclosporin toxicity.