Studies that have led to novel insights into the molecular bases of vasopressin and oxytocin receptor functions are reviewed. General structural features, structural bases of ligand binding and domains conferring G protein-coupling selectivity are discussed. It is concluded that this understanding of receptor function at a molecular level is of importance in the development of new molecules with high selectivity for the different subtypes of receptors, and thus in the development of molecules of therapeutic interest. The current clinical implications, such as in the treatment of preterm labour and diabetes insipidus are highlighted.