Arginine vasopressin (AVP) and arginine vasotocin (AVT) influence social behaviors in a number of species from diverse taxonomic groups, therefore suggesting a conservation of social functions for these homologous neuropeptides during vertebrate evolution. However, whether or not AVP has the ability to directly influence social behavior in humans has not yet been determined. Because influences of AVT/AVP on behaviors related to social communication, particularly in aggressive contexts, are among the most consistently observed across species from diverse vertebrate groups, the present study was designed to determine if AVP administration would influence cognitive, autonomic and/or somatic responses to species-specific social stimuli important for agonistic communication in humans. Specifically, we tested the effects of intranasal AVP administration on attention towards emotionally expressive facial expressions, as well as on heart rate (HR), skin conductance (SC) and corrugator supercilii electromyograms (corrugator EMG) in response to these social stimuli. AVP did not affect attention toward, nor autonomic arousal in response to, emotionally neutral, happy or angry facial expressions, but it did selectively enhance the corrugator EMG responses evoked by emotionally neutral facial expressions, making them similar in magnitude to responses evoked by angry facial expressions in control subjects. Because this muscle group is involved in agonistic communication, these results suggest that AVP may influence aggression in human males by biasing individuals to respond to emotionally ambiguous social stimuli as if they were threatening/aggressive.