A review of the regulating effect of RAAS on electrolyte and H2O balance and on blood volume and pressure, a resultant of its components, the renin-angiotensin system and aldosterone.Evaluation of RAAS and K balance is important in determining the causes of hypertension and its control.When the plasma renin activity (PRA) is low, spironolactone may be useful; when PRA is high, propranolol may be helpful.Extensive references are available.