This experiment examined the hypothesis derived from the social categorization perspective that intergroup cooperation reduces bias by transforming members' cognitive representations of the aggregate from 2 groups to 1 group. Two 3-person groups experienced intergroup contact under conditions that varied (a) member's representations of the aggregate as 1 group or 2 groups (without involving cooperation) and (b) the presence or absence of intergroup cooperation. As expected, in the absence of cooperation, bias was lower among Ss induced to conceive of the 6 participants as 1 group rather than as 2 groups. Also as predicted, among Ss in the 2-groups condition, intergroup cooperation increased the strength of the 1-group representation and decreased bias. Multiple regression mediation analysis revealed, as expected, that members' representations mediated bias and that the 1-group representation primarily increased the attractiveness of former outgroup members. (PsycINFO Database Record (c) 2016 APA, all rights reserved)