Ambulatory blood pressure and heart rate responses were obtained in 33 male paramedics during a 24-hour work shift to examine the effects of episodes of occupational stress on cardiovascular reactivity and subjective reports of stress. The aim of this study was to determine how individual differences in cynical hostility and defensiveness interacted with situational demands to affect cardiovascular responses in a natural setting. Defensiveness was found to interact significantly with cynical hostility in predicting subjects' heart rate responses in different work contexts. Specifically, in a hospital setting involving interpersonal conflict, subjects who were high in both defensiveness and hostility showed heart rate responses approximately 10 bpm higher than subjects who were high in hostility but low in defensiveness. The same pattern of relationships was obtained for diastolic blood pressure. High and low hostile subjects were also found to differ from each other in their daily mean levels of ambulatory blood pressure during awake and sleep periods. These findings obtained in a natural setting lend further support to the significance of cynical hostility for cardiovascular reactivity. The results for defensiveness suggest the need for further research on the role of conflicting attitudes in the pathophysiology of cardiovascular diseases.