Problems with conventional blood pressure measurement using the mercury sphygmomanometer, related to both equipment and technique, are discussed. The effect of observer bias on the measuring procedure is also considered. Blood pressure variability and the phenomenon of 'white coat' hypertension are then described and their impact on the interpretation of hypertensive cardiovascular risk is emphasized. The potential role of electronic sphygmomanometers, and the use of ambulatory BP monitoring equipment, to overcome some of these problems is analysed. Technical factors both in use and interpretation of ambulatory BP data are considered, emphasizing the lack of prospective data and the difficulties in defining a 'normal' range. The current role of such equipment in both research and clinical practice is defined.