The discovery of new signalling pathways is always followed by the development of pharmacological agents as drugs that can be used in the treatment of diseases resulting from a dysfunction of the signalling pathway in question. Apelin signalling plays a role in the central and peripheral regulation of the cardiovascular system, in water and food intake, and possibly in immune function. Up-regulation of ligand and receptor is also associated with pathophysiological states such as cardiac dysfunction and neovascularisation. Finally, the apelin receptor is a coreceptor for the entry of several HIV-1 and SIV strains. In view of these features, the apelin receptor constitutes a very interesting target for the design of new drugs for treating the prime causes of human mortality.