1. Serial measurements of plasma renin activity (PRA), plasma aldosterone concentration (PA) and blood pressure were performed overnight in patients with borderline (group 1) and sustained essential hypertension (group 2) before and after acute and chronic administration of either propranolol or pindolol.
2. Group 1 patients exhibited a typical rhythm of recumbent PRA with low values before midnight and large increases early in the morning.
3. In contrast, no rhythm and very low PRA values were observed in patients of group 2. Blood pressure was higher in group 2 than in group 1. There was a significant correlation between the hyporeninaemic and hypotensive effect of either acute (r = 0·79) or chronic (r = 0·4) β-receptor blockade.
4. In group 1, after β-receptor blockade the day—night profile of renin was similar to that observed in group 2 before treatment. Thus, in this latter subgroup, low-renin profiles might reflect reduced β-adrenoreceptor activity.
5. Plasma aldosterone was lower in group 2 but appeared to be inappropriately high relative to renin.
6. The data suggest that in hypertensive patients classified according to their blood pressure and recumbent PRA profiles a significant relationship exists between changes in PRA and arterial pressure. Thus patients with high PRA respond better to treatment than patients with low renin. We conclude that in the patients studied sympathetic nervous system activity mainly determined renin values as well as anti-hypertensive effectiveness of the β-blocking drugs.