Ambulatory blood pressure monitoring(ABPM) permits 24-hour measurement of blood pressure(BP) without restricting the subject's activities. The tilting test is used to evaluate BP variability and autonomic nervous responses, especially baroreceptor reflex sensitivity(BRS) during changes of body position. The change of BP and BRS are common to both ABPM and the tilting test. In this instance, BRS is expressed as the ratio between heart rate(HR) variation and systolic BP variation(delta RR/delta SBP). The results were the same as those produced by all other tests including sequential method, squatting test, the neck chamber method, and tilting test. Therefore, we investigated the correlation between BRS and BP changes monitored mainly by means of ABPM. Twenty-four-hour BP variation(SD) manifest both short-term variability(SDh), and long-term variability extending over 24 hours(SD24) (SD2 = SDh2 + SD24(2). In the former case(SDh), atherosclerosis and lowered BRS participate, and in the latter case(SD24), activation of the sympathetic nervous system(SNA) participates strongly. Each BP value during 24 hours(Pi: i = 1, 2, ... 10(5)) is expressed by the product(Pi = phi i x P0) of the ratio of variability(phi i) and sleep-time base BP(P0) values. The phi i is expressed by HR variation and two elements: the cardiovascular response element and the BRS element. In mild cases of essential hypertension, the correlation between Pi and HR variation is high. In severe cases of essential hypertension and in cases of Shy-Drager syndrome, short-term phi i caused by BRS decrease is large, and the correlation between phi i and HR variation during 24 hours drops. Although measuring short-time variability indirectly with ABPM is impossible, BRS can be evaluated on the basis of the product(BI) of diastolic BP(Pd) and pulse interval(RR). The multi-biomedical recorder(TM2425, A&D, Co.) permits 24-hour monitoring of body position and daily activities(acceleration), simultaneous with evaluation of BI, which is related to autonomic nervous activity and BRS. Its employment is, therefore, considered clinically useful.