Abstract
Eleven patients with essential hypertension were treated with hydrochlorothiazide/KCl for three months. A significant fall in total blood volume, exchangeable sodium and blood pressure could be demonstrated both after one to two weeks and after three months of treatment, while a fall in serum sodium and body weight was only significant after one to two weeks of treatment. Thus, hypovolemia may, perhaps, be the explanation for the antipressor effect of thiazide even after three months of treatment.