In a prospective study blood pressure was recorded for 20 years in 132 white patients with congenital blindness and in 138 white control schoolchildren. The subjects for both groups were consecutively enrolled without any selection parameters. During the study period a similar proportion of blind patients and controls reported identical consumption of tobacco (above the age of 14 years) and of oral contraceptives (above 21 years) among women. Mean 24-h urinary sodium excretion, collected randomly in both groups, did not differ between the blind patients and the controls. During the 20-year period systolic and diastolic blood pressure rose with age in the control group as expected and much less in blind patients; after 14-17 years the difference was statistically significant. The mean slope of the regression line (beta coefficient) for systolic blood pressure versus age was 1.143 in the blind patients and 1.794 in the controls (P less than 0.001), and for diastolic blood pressure 0.908 in the patients and 1.353 in the school children (P less than 0.001). The mean weight and body mass index increased more in the blind patients than in the controls (difference 5.9 and 2.8 kg, respectively). The results support the hypothesis that low visual and cognitive stress levels determine a lower level of cardiovascular reactivity with ageing.