In explaining differences between groups, people ascribe the human essence to their ingroup and consider outgroups as less human. This phenomenon, called infra-humanization, occurs outside people's awareness. Because secondary emotions (e.g. love, hope, contempt, resentment) are considered uniquely human emotions, people not only attribute more secondary emotions to their ingroup than to outgroups, but are reluctant to associate these emotions with outgroups. Moreover, people behave less cooperatively (in terms of altruism, imitation, and approach) with an outgroup member who expresses himself through secondary emotions. Infra-humanization occurs for high and low status groups, even in the absence of conflict between groups. It does not occur when the outgroup target is adequately individualized, by a complete name or through perspective taking, for instance. The differential familiarity with the ingroup and the outgroup cannot explain infra-humanization. Yet, preliminary results show that subjective essentialism and ingroup identification may mediate the effects of infra-humanization. A connection is made between nationalism and infra-humanization. Copyright © 2003 John Wiley & Sons, Ltd.