1. The influence of age on the rate of spillover of noradrenaline into plasma, clearance of noradrenaline from plasma, and plasma noradrenaline concentration at rest was studied in 34 healthy subjects aged 20–69 years.
2. The plasma concentration of noradrenaline was dependent on age, values being higher in older subjects.
3. This age-dependence of plasma noradrenaline concentration was due principally to a reduced clearance of noradrenaline from the circulation in older subjects.
4. The rate of spillover of noradrenaline into plasma was little influenced by age. The higher plasma noradrenaline values found in older subjects do not seem to be due to an increase in sympathetic nervous system tone with aging.