It is now possible to record numerous ambulatory blood pressures by a noninvasive method using the Remler, a portable semi-automatic device. The blood pressure profiles obtained with this recorder in hypertensive patients during customary daily activities have revealed the existence of a circadian blood pressure variation. Thus, blood pressure is highest in the morning, lowest early in the afternoon and tends to increase again late in the afternoon. This circadian variation is not modified by treatment with diuretics and/or betablockers. These blood pressure recordings also made it possible to establish that antihypertensive therapy with these agents does not modify blood pressure variability over the day.