Charismatic leaders have had tremendous effects on the fortunes and fates of individuals and societies across the world. Via verbal and nonverbal signaling, such leaders form profound emotional bonds with followers. Despite evidence for its powerful effects, we know very little about what facilitates the charismatic relationship. Here, we argue that the neuropeptide oxytocin (OT), known to be implicated in parent–child attachment, also enhances the effects of charismatic leaders in groups. In a double-blind placebo-controlled study, we administered intranasal OT to participants, led by a confederate trained to exhibit charisma, and monitored participants’ responses to the confederate’s signaling while leading a group task. We found that OT enhanced the effects of 3 common manifestations of charismatic signaling—verbal behaviors, nonverbal behaviors, and followers’ perceptions of the confederate’s charisma—on classic outcomes of charismatic influence. Specifically, participants under OT showed more expressions of positive affect and mimicry of the leader in response to the confederate’s signaling, and perceptions of the confederate’s charisma had stronger effects on participants’ willingness to trust each other. These findings extend the role of OT beyond the attachment bond to explain leader–follower relationships, shed light on the role of neuroendocrine factors in contagion processes in groups, and support the social saliency perspective of OT. We note, however, that because charisma was not manipulated, we had reduced control over the confederates’ specific behaviors. We address this limitation in the Discussion, point to broader theoretical implications of our work, and offer ideas for future research.