People exhibit group reciprocity when they retaliate, not against a person who harmed them, but against another person in that person's group. We tested for group reciprocity in laboratory experiments. Subjects played a Prisoner's Dilemma with partners from different groups. They then allocated money between themselves and other participants. In punishment games, subjects whose partner had defected punished participants from the partner's group more, compared to their punishment of participants from a third group. In dictator-style games, subjects did not exhibit group reciprocity. We examine possible correlates of group reciprocity, including group identification and cooperativeness.