After an agonistic conflict between two animals, they may exchange affiliative social contacts. The function of this reconciliation behavior is thought to be the repair of the social relationship between the two opponents. We examined the hypothesis that reconciliation is socially effective because it may also lead to a reduction of the victim's acute stress. Reconciliation was studied in a well-established captive group of long-tailed macaques (Macaca fascicularis). The behavior of the victim in a 10 min period after the end of an agonistic interaction was recorded and compared with that of a control observation made on the same animal the next day. The tendency to reconcile was elevated above control levels only during the first 3 min. Reconciliation led to a fast reduction in scratching rates and to a decrease of the reoccurrence of aggression received. Losers took the initiative to reconcile more than expected. Dominants granted reconciliation depending on their relatedness with the victims and on the quality of the relationship with them. After those interactions in which contra-aggression and no clear submission occurred, the reconciliation rate was remarkably high. These results suggest that reconciliation can be an effective means to reduce the victim's acute stress and that its function in repairing social relationships can partly be mediated by its physiological effects. The intimate relation between the quality of the social relationship and the conciliatory tendency can be extrapolated to explain interspecific variation.