The similarities of 30 young (X = 26 years) and 30 middle-aged (X = 52 years) spouse pairs in behavioral and cardiovascular response to two experimental stressors were compared to assess the importance of shared home experiences in determining cardiovascular responsivity to stress. Familial environmental influences on reactivity should produce increasing similarity among family members with number of years lived together. Although pair members exhibited a number of behavioral similarities, some of which appeared to increase with number of years lived together, there were few similarities in heart rate and blood pressure response to stress. However, both young and middle-aged pairs exhibited significant similarities in systolic blood pressure response to isometric handgrip. The fact that similarities were observed in young as well as middle-aged spouse pairs suggests that assortative mating in regards to cardiovascular reactivity to stress may occur in some instances. As a result, some previous estimates of the heritability of cardiovascular reactivity to environmental stress may have been artificially low.