The epidemiology of a common measure of cardiovascular reactivity, the change in systolic blood pressure (DeltaSBP) from the supine to the standing position, is described in a cohort of 13 340 men and women aged 45 to 65 years enrolled in the Atherosclerosis Risk in Communities (ARIC) Study. The distribution of DeltaSBP was found to be symmetrical and unimodal, with a mean value near zero (-0.45 mm Hg). The range of DeltaSBP was from -63.2 to 54.3 mm Hg, and the standard deviation was 10.8. Stratification of DeltaSBP by race and gender shows a slight shift in distribution toward higher values for black men and women. DeltaSBP was categorized into deciles. Participants in the top 30% and bottom 30% of the distribution were compared with individuals in the middle 40% of the distribution, who had little or no change in SBP on standing. Participants in the bottom 30% (ie, SBP decreased on standing) were significantly older, had a greater prevalence of hypertension and peripheral vascular disease, had higher values of SBP, and had more cigarette-years of smoking. Among participants in the top 30% (ie, SBP increased on standing), a significantly larger proportion were black, mean seated SBP was higher, and the predicted risk of developing coronary heart disease after 8 years was greater. The response of SBP to change in posture showed considerable variability in a population sample of middle-aged adults. Cardiovascular morbidity, sociodemographic factors, and cigarette smoking were associated with the magnitude and direction of the postural change.