It is well established that hypertensive patients benefit from drug treatment of their disorder. In recent years three major out-come studies of antihypertensive treatment in elderly hypertensives have shown substantial benefits, i.e. a reduction in the risk of stroke and other cardiovascular mortality and morbidity. In all these studies beta-blockers and/or diuretics were used in comparison with placebo. Newer therapeutic alternatives have, however, at least theoretically, many advantages which could result in further improvements in prognosis. The initial Swedish Trial in Old Patients with Hypertension (STOP-Hypertension 1) was conducted in men and women aged 70-84 years. STOP-Hypertension 2 will evaluate the therapy used in STOP-Hypertension 1 against therapy based on either ACE-inhibitors (enalapril and lisinopril) or on calcium antagonists (isradipine and felodipine), using the PROBE design (Prospective, Randomised, Open, Blinded Endpoint evaluation). The primary aim will be to assess the effect on cardiovascular mortality. Statistical calculations indicate that 6,600 patients, followed for four years will be needed (2p < 0.05, power 90%) to obtain significance if there is a 25% difference between the new and the established therapy. Patients in primary health care (300 centres) will be included if their supine blood pressure is > or = 180/105 mmHg (and/or). Recruitment of patients started in September 1992 and so far more than 100 patients/week have been included.