1. Plasma adrenaline and noradrenaline were measured in supine and upright positions in 27 essential hypertensive patients and in 12 age-matched control subjects.
2. Plasma adrenaline was markedly increased in a large proportion of patients, compared with control subjects, either in supine or in upright positions, whereas no significant differences were found in plasma noradrenaline.
3. Six hypertensive patients were chronically treated with β-adrenoreceptor-blocking agents (five with propranolol and one with pindolol). Plasma noradrenaline was not significantly changed in the supine position but was markedly increased on standing in four out of six patients. Plasma adrenaline was decreased in five out of six patients either in supine or upright positions.
4. These findings support the view that the adrenergic system participates in the mechanism of essential hypertension.