1. Plasma catecholamines and adrenergic correlates of cardiac function were compared in young men with borderline hypertension, classified according to renin status (group 1). Plasma catecholamines were increased and cardiac pre-ejection periods were shortened in ‘high’-renin patients.
2. Plasma catecholamines were raised in 70% of ‘high’-renin patients with primary hypertension (group 2), were related directly with age in normotensive females and were related inversely with catecholamine responses to postural stress in both normotensive and hypertensive subjects (P < 0·01).
3. The raised catecholamines of four ‘high’-renin patients with pronounced features of sympathetic nerve activity-caricatures were elevated further during hypertensive periods. Mean arterial blood pressures were reduced 20–30% after either α- or β-receptor blockade. Catecholamines were reduced after β-receptor blockade.
4. There appears to be a spectrum of neurogenic ‘gain’ in primary hypertension; it is suppressed in ‘low’-renin hypertension, directly related to blood pressure in ‘normal’-renin hypertension, increased in ‘high’-renin hypertension and achieves a maximum in caricatures. Neurogenic factors seem to be important in the cause and maintenance of ‘high’- and ‘normal’-renin hypertension respectively. The caricatures may be examples of a severe form of hypothalamic stimulation.