1. The 24 h urinary excretion of adrenaline, noradrenaline, normetadrenaline, metadrenaline and vanilloylmandelic acid has been compared in 17 male normotensive subjects and 25 age-matched male hypertensive patients studied under similar in-patient conditions.
2. 24 h urinary metadrenaline was significantly lower in the hypertensive patients. With this exception, no significant differences were found between the two groups when the total 24 h excretion of free catecholamines and their metabolites was analysed.
3. Diurnal variation in free catecholamine excretion was found in both normotensive and hypertensive subjects. There was no corresponding variation in metabolite excretion.
4. No correlation could be established between systolic or diastolic blood pressure and the amounts of the catecholamines or their metabolites in the urine of either group.
5. The results are considered in the light of recent work demonstrating high plasma catecholamine concentrations in hypertension. They lend no support to the concept that excessive circulating catecholamines are responsible for the elevated blood pressure in essential hypertension.