Two experiments examined the impact of positive mood on impression formation about in-group and out-group members. Participants performed a dot estimation task and received feedback that they belonged either to the group of overestimators or underestimators. They rated the likability of target persons characterized by positive or negative traits and, in half of the trials, by their group membership (overestimators or underestimators). These judgments were made either in an unmanipulated neutral mood state or after induction of a positive mood. Both experiments revealed a stronger in-group-out-group differentiation in a positive mood than in a neutral mood. Without group label presented, the impact of the individuating information was the same in both mood states; with group label presented, it was smaller in positive mood. Response latencies did not vary with mood. The data demonstrate a twofold impact of mood, due to both its informational function and its enhancement of the categorizing information's weight.