Two multicenter European trials studying the correlation between ambulatory blood pressure and long-term prognosis of hypertension are at present underway. The Office versus Ambulatory trial (OvA) has accepted primary hypertensives of all ages, with systolic and diastolic hypertension; in the Systolic Hypertension in the Elderly study (Syst-Eur) only elderly patients with systolic hypertension are being studied. In both trials, blood pressure is being recorded at intervals of 30 min over 24 h, using fully validated non-invasive recorders. Treatment in both studies is based on office blood pressure. As both studies are expected to answer many current questions on the value of ambulatory blood pressure recordings, participation is strongly encouraged.