This study examined whether social support can reduce cardiovascular reactivity to an acute stressor. College students gave a speech in one of three social conditions: alone, in the presence of a supportive confederate, or in the presence of a nonsupportive confederate. Systolic and diastolic blood pressure were measured at rest, before the speech, and during the speech. While anticipating and delivering their speech, supported and alone subjects exhibited significantly smaller increases in systolic and diastolic blood pressures than did nonsupported subjects. Supported subjects also exhibited significantly smaller increases in systolic blood pressure than did alone subjects before and during the speech. Men had higher stress-related increases in blood pressures than did women; but gender did not moderate the effects of social support on cardiovascular reactivity. These results provide experimental evidence of potential health benefits of social support during acute stressors.