1. The relationship of basal plasma noradrenaline to blood pressure, age, sex, urinary sodium excretion, and plasma volume has been examined in 117 untreated ambulatory patients with essential hypertension.
2. No significant correlations between basal plasma noradrenaline and either age or sex were apparent in the total group of essential hypertensive patients. In addition, no significant correlations were observed between plasma noradrenaline and 24 h urinary sodium excretion.
3. Basal plasma noradrenaline concentration was significantly higher in high renin essential hypertensive subjects compared with those with normal or low plasma renin activity.
4. Plasma noradrenaline was reduced significantly in relatively young patients with low renin essential hypertension, but appeared to be normal in other low renin subjects.
5. Basal plasma noradrenaline correlated significantly with blood pressure in patients with normal or low renin essential hypertension but the relationships were only significant in male patients.
6. No significant relationship between basal plasma noradrenaline and either blood pressure or plasma volume could be demonstrated in this population of essential hypertensive patients.