IN recent years the benzothiadiazine diuretics have become the drugs of choice for treating mild to moderate hypertension. Although their anti-hypertensive effect is relatively weak, they are quite non-toxic and are well absorbed orally. The mechanisms by which these agents reduce blood pressure in hypertensive individuals are not known. Some investigators1,2 have implicated natriuresis as the primary event, whereas others3 have suggested that the concentration of circulating pressor agents is reduced. That benzothiadiazine diuretics do antagonize in vitro intestinal and aortic contractions has already been demonstrated4,5. Consequently, the possibility exists that these agents directly affect the responsiveness of vascular smooth muscle. It was, therefore, considered of interest to try to dissociate the anti-hypertensive and diuretic actions of these compounds and, further, to intensify the former action while minimizing the latter.