A study protocol for a double-blind randomised control trial of hypotensive treatment in elderly hypertensive patients has been tested in a number of pilot centres throughout Europe. It was shown that this study is possible from the logistic point of view. In these elderly patients, hydrochlorothiazide + triamterene treatment with or without methyldopa, maintained a significant hypotensive effect in the absence of major electrolyte disturbances. The initiation of hypotensive therapy did not provoke an excess of cardiovascular complications. The influence of hypotensive therapy on the general well-being and on the morbidity and the mortality of elderly patients with high blood pressure, is thereby being assessed. The study will continue for 5 years and other centres are invited to join.