OBJECTIVE This study examined aspects of the transactional model of hostility and health by investigating relationships among hostility, interpersonal interactions, and ambulatory blood pressure in a healthy community sample. METHODS Participants included 65 female and 39 male healthy adults between the ages of 18 and 46 years. Ambulatory blood pressure (ABP) and diary data on mood and social interactions were obtained every 20 minutes for 1 day. Mixed models regression analyses were used to evaluate the relationships among hostility, interpersonal interactions, and ABP. RESULTS Trait hostility was positively associated with the frequency and intensity of negative interactions and was negatively associated with the frequency and intensity of positive interactions. Interacting with others was associated with increases in systolic blood pressure (SBP) and diastolic blood pressure (DBP). The magnitude of the increase in blood pressure was positively associated with the degree to which the interaction was perceived as negative. Hostility was not directly associated with ABP/heart rate (HR) or ABP/HR responses during any interactions or negative interactions. However, there was an interaction between hostility and negative interaction intensity for DBP, suggesting that hostility moderates the effects of negative interactions on DBP. Specifically, increases in the intensity of negative interactions were associated with increases in DBP for participants with high, but not low, hostility. CONCLUSIONS The results provide partial support for the notion that hostility may be associated with risk for cardiovascular disease through its effects on interpersonal interactions and their cardiovascular correlates.