In 38 hospitalized patients with uncomplicated essential hypertension intra-arterial pressure was recorded continuously for 24 hours with the Oxford technique. On the basis of beat by beat analysis, hourly and 24-hour means of mean arterial pressure (MAP) and heart rate (HR) were obtained. The standard deviations and variation coefficients of the hourly means were used as a measure of absolute and relative blood pressure variability respectively. By randomization patients were ambulant during the day (group A; n = 19) or they were restricted to bed (group B). The patients of group B were sensory deprived during the first 4 hours of the blood pressure recording. During the night MAP, HR, and their respective variabilities were similar for both groups. During bed rest MAP was reduced as compared to ambulant values (P less than 0.05), but bed rest had no effect on HR, or on the variability of HR and MAP. During concomitant sensory deprivation HR and the variability of MAP and HR all declined to nightly values, though MAP did not change. In group B, HR-variability (absolute and relative) was inversely correlated to age, but no relationship between these two parameters was observed in group A. During concomitant sensory deprivation, but not during bed rest alone or during night rest, relative MAP-variability was also inversely correlated to age. It is concluded that sensory stimuli have an important effect on HR and on the variability of MAP and HR, but not on MAP itself, indicating that to some extent blood pressure and its variability are regulated independently.