Increasing attention is being given to cardiovascular reactivity as a marker and potential risk factor for disease. Individual differences in cardiovascular reactivity to laboratory stress have been assessed in hypertensive adults and matched normotensive controls, in the normotensive offspring of hypertensive parents, and in twin-family studies of normotensive adolescents and adults. Cardiovascular stress reactivity is a relatively stable characteristic of individuals, and exaggerated stress-responsivity, associated with a positive family history of essential hypertension, is demonstrable early in life. Classic twin studies document significant genetic influences on cardiovascular stress patterns, and longitudinal studies suggest that heightened reactivity to stress constitutes a risk factor for the development of sustained hypertension. The study of stress reactivity may lead to early identification of young pre-hypertensive individuals who are candidates for behavioral and other nonpharmacologic intervention efforts.