BACKGROUND: Both social support and hostility have been reliably associated with important health outcomes including coronary heart disease (CHD). One potential pathway by which these variables may influence CHD is via their impact on cardiovascular reactivity (CVR). Although social support has been generally associated with beneficial effects on cardiovascular functioning, the cynicism and mistrust among hostile individuals may prevent them from benefiting from the support process during times of stress. PURPOSE AND METHOD: The present study examined if level of hostility influenced CVR when discussing positive or negative personal experiences with a friend. To test this, healthy males and females and their same-sex friend were recruited (N = 216) and randomly assigned to discuss either a positive or negative (stressful) personal experience while cardiovascular measures were recorded. RESULTS AND CONCLUSIONS: Results revealed the greatest systolic blood pressure and diastolic blood pressure reactivity among individuals high in hostility when discussing a negative experience. These results suggest that hostility may interfere with the benefits from support transactions during stress. Likewise, this association between hostility and reactivity was apparent for both support recipients and support providers, suggesting that hostility could undermine the health benefits of both aspects of support transactions.