Ageing is an important risk factor for the development of cardiovascular diseases. Vascular ageing is mainly characterized by endothelial dysfunction, an alteration of endothelium-dependent signalling processes and vascular remodelling. The underlying mechanisms comprise increased production of reactive oxygen species (ROS), inactivation of nitric oxide (.NO) and subsequent formation of peroxynitrite (ONOO(-)). Elevated ONOO(-) may exhibit new messenger functions by post-translational oxidative modification of intracellular regulatory proteins. Mitochondria are a major source of age-associated superoxide formation, as electrons are misdirected from the respiratory chain. Manganese superoxide dismutase (MnSOD), a mitochondrial antioxidant enzyme, is an integral part of the nucleoids and may protect mitochondrial DNA from ROS. A model linking .NO, mitochondria, MnSOD and its acetylation/deacetylation by sirtuins (NAD+-dependent class III histone deacetylases) may be the basis for a potentially new powerful therapeutic intervention in the ageing process.