Psychosocial stress precipitates a wide spectrum of diseases with major public-health significance. The fight-or-flight response is generally regarded as the prototypic human stress response, both physiologically and behaviorally. Given that having positive social interactions before being exposed to acute stress plays a preeminent role in helping individuals control their stress response, engaging in prosocial behavior in response to stress (tend-and-befriend) might also be a protective pattern. Little is known, however, about the immediate social responses following stress in humans. Here we show that participants who experienced acute social stress, induced by a standardized laboratory stressor, engaged in substantially more prosocial behavior (trust, trustworthiness, and sharing) compared with participants in a control condition, who did not experience socioevaluative threat. These effects were highly specific: Stress did not affect the readiness to exhibit antisocial behavior or to bear nonsocial risks. These results show that stress triggers social approach behavior, which operates as a potent stress-buffering strategy in humans, thereby providing evidence for the tend-and-befriend hypothesis.