In this study we investigated the effects of nonevaluative social interaction on the cardiovascular response to psychological challenge. Thirty-nine college-age females appeared accompanied (“Friend” condition) or unaccompanied (“Alone” condition) to an experimental laboratory. In the Friend condition, partners were present while the subject participated in two laboratory tasks, and the partners' evaluation potential was minimized by design. Subjects in the Friend condition showed reduced heart rate reactivity to both tasks, relative to the Alone group, an attenuated task-related systolic blood pressure response to one of the tasks, and a reduced diastolic blood pressure increase during a solitary interview. In two other instances, partner-related response reductions were apparent only for Type A subjects. None of these effects was accompanied by differences in task performance or self-reported emotional response. Interpersonal support may reduce cardiovascular responsivity to stress, an effect with possible implications for understanding the association between social relationships and cardiovascular risk.