To evaluate the hypotensive efficacy of labetalol (600 mg/day) six mild to moderate hypertensive patients were studied by the indirect continuous blood pressure monitoring with the Del Mar Avionics Pressurometer 111 degrees. This technique gives a much larger number of blood pressure values in a greater variety of conditions than the conventional Riva-Rocci sphygmomanometer. After one month of continuous therapy there was a substantial reduction in systolic and diastolic pressure. The increased index of Kurtosis revealed a decreased blood pressure variability. The circadian changes of blood pressure were not significantly affected, but the morning peak was smoothed by labetalol.