Thirty-two groups of three subjects each participated once in an intergroup public goods game (IPG) in which two groups compete for the provision of step-level public goods. Half of the groups were allowed to discuss the conflict before their members decided privately and anonymously whether to contribute their endowments to their group benefit, and half were not given this opportunity. The results show that preplay group discussion enhances the percentage of contributors and changes the players' estimates about the decisions of the other players. The theoretical implications of the results are examined within the framework of a new model which relates the individual decision to contribute or not to the reward structure, altruism, and the individual's belief structure.