This article reviews the contributions of laboratory-based reactivity testing and ambulatory blood pressure monitoring in the evaluation of the role of psychosocial factors in hypertension. Reactivity testing is ideally suited for evaluating individual differences in susceptibility to the acute effects of stressors but cannot resolve the question regarding whether stressors in everyday life contribute to a sustained elevation of pressure. Although several associations between increased reactivity and hypertension have been demonstrated, they do not necessarily imply a primary role for behavioral factors. Ambulatory monitoring is ideally suited for studying the effects of everyday stressors and has shown that blood pressure may increase as a result of occupational stress. On the grounds that hypertension results from an interaction of genetic and environmental factors, it is argued that both techniques have their place and that the role of psychosocial factors can best be demonstrated by prospective studies of persons exposed to different levels of stress.