Ageing is associated with a reduction in appetite and food intake, which has been termed the 'anorexia of ageing'. After age 70-75 years average body weight decreases, even in healthy people, disproportionately due to loss of lean tissue. The 'physiological' anorexia and weight loss of ageing predispose to pathological weight loss and malnutrition. Marked weight loss is common in the elderly and a major cause of morbidity and increased mortality. The cause(s) of the anorexia of ageing are largely unknown. We have identified several possibilities. Animal and preliminary human studies indicate that ageing is associated with increased satiety factors and a reduced feeding drive. Endogenous opioids stimulate eating. We administered i.v. infusions of the opioid antagonist naloxone to young and older adults. Overall, the suppression of food intake was not different in the two age groups, but was increased in older women, suggesting reduced stimulation of feeding by endogenous opioids in this group. Plasma concentrations of the satiety hormone cholecystokinin (CCK) increase with ageing. Intravenous CCK-8 infusion produced greater suppression of food intake in older than young subjects (33.5 vs 15.5% P = 0.026), indicating that sensitivity to the satiating effects of CCK is at least maintained and may increase with age. This raises the possibility of using CCK antagonists as stimulants of appetite and food intake in malnourished older people.