Age influences virtually all known physiological steps in the pathway of cortical and hypothalamic regulation of thirst and water balance, including posterior pituitary secretion of AVP, baroreceptor action mediated by pressure sensors in great vessels in the neck, concentrating capacity of renal tubules, and coregulators of salt and water balance, such as renin, aldosterone, and atrial natriuretic hormone. Ageing seems to blunt water-seeking behaviour and augment brain output of AVP. Ageing is associated with a decrease in plasma volume of approximately 7%, and a decrease in plasma volume of approximately 10%. Abbreviations: AVP, arginine vasopressin; PVN, paraventricular nucleus; SCN, suprachiasmatic nucleus.