Our studies have shown that (1) automatic blood pressure readings obtained from portable monitors do not induce any alerting reaction or pressor response in the patient; (2) although the measurements are intermittent, non-invasive ambulatory blood pressure monitoring is able to provide a true estimate of 24-h blood pressure and heart rate mean values (the assessment of 24-h blood pressure and heart rate variabilities is less accurate); (3) the nocturnal fall in blood pressure is not altered by the possible disturbance to the patient's sleep induced by repeated cuff inflations; and (4) even when the automatic blood pressure readings obtained are similar to simultaneous readings obtained by a sphygmomanometer, the accuracy of the values provided by portable monitors used in truly ambulatory conditions cannot be taken for granted. These findings have particular implications for the cost: benefit ratio if ambulatory blood pressure monitoring is to be used in the routine evaluation of hypertensive patients.