1. Six essential hypertensive patients (five with low renin) were treated in successive weeks with placebo; hydrochlorothiazide 100 mg (382 μmol)/day; hydrochlorothiazide and 50 mmol of sodium/day diet; hydrochlorothiazide, 50 mmol of sodium diet and propranolol 160 mg (544 μmol)/day; and hydrochlorothiazide, 50 mmol of sodium and indomethacin 100 mg (287 μmol)/day.
2. Although blood pressure remained unchanged and serum potassium fell on diuretic with or without low salt, there was a marked increase of active renin and a lesser increase of inactive renin, resulting in an increased proportion of active to total renin.
3. Propranolol decreased both active and inactive renin, but not significantly.
4. Indomethacin produced a marked suppression of active renin, a smaller reduction in inactive renin, and a reduction of the ratio of active to total renin almost to placebo values.
5. Blood pressure rose to control values on indomethacin despite the fall in renin whereas it fell with propranolol with little change in renin.
6. Serum aldosterone rose with stimulation but remained elevated despite effective renin suppression with indomethacin and continuing reduced serum potassium concentration.