Physiologic responses to environmental stress show striking interindividual differences, beginning early in life. Whereas cardiovascular reactivity (CVR) to stress has been linked to short- and long-term changes in health, little previous work has addressed reactivity in children, and no past studies have investigated the relationship of reactivity to psychosocial factors, such as stressful life events (LE) and social support (SS). We therefore studied cardiovascular response to psychologically and physically stressful laboratory tasks in 25 adolescent boys. The degree of individual CVR was examined cross-sectionally in relationship to LE, SS, and "sense of permanence" (SP), a construct reflecting the stability or continuity in the child's life experience. Heart rate reactivity (HRR) and mean arterial pressure reactivity (BPR) were bimodally distributed, with a subpopulation of approximately 20% of subjects demonstrating an exaggerated cardiovascular response. SP was related to BPR at a borderline level of significance (R = 0.33, p less than 0.10), whereas SS was unrelated to either reactivity variable. Unexpectedly, LE was strongly and inversely related to both HRR and BPR (R = -0.40 and -0.47, respectively, p less than 0.05). Subjects reporting low numbers of previous stressful life events had the highest level of cardiovascular reactivity. Possible explanations for this finding included (1) the development of a hyperdynamic response as a consequence of avoiding or denying stressful experience, (2) an effect of exaggerated CVR on cognition and the reporting of stressful events, or, most plausibly, (3) an 'inoculation effect,' in which previous LE facilitate the development of effective coping strategies, thereby diminishing responses to stressful laboratory tasks.