This study tested the hypothesis that partisanship influences judgments of fairness and trustworthiness in the mediation of social conflict. Subjects evaluated third patty proposals for resolving the conflict in Jerusalem. A 2 x 2 x 4 factorial design examined (1) partisanship of the subject, either partisan (pro-Israeli) or nonpartisan (neutral); (2) content bias of third party proposals, where the substance of the proposal was either (a) pro-Israeli or (b) evenhanded; and (3) source bias, where the third party was labeled as being (a) pro-Israeli, (b) pro-Palestinian, (c) neutral, or (d) of unknown persuasion. Analyses of judgments of fairness and third patty trustworthiness indicated differences between partisan and nonpartisan subjects in self-serving bias and underlying dynamics in judgments, Partisans used favorableness of the proposals to judge the trustworthiness of the third party, independent of evenhandedness of the proposal, whereas evenhandedness was the criterion for nonpartisans. Nonpartisans trusted the neutral third party and partisans trusted the pro-Israeli third party regardless of proposal fairness, Partisans showed a cushioning effect of third party characteristics: a pro-Israeli third patty who made an evenhanded proposal (relatively unpalatable to the pro-Israeli subjects) was trusted more than a pro-Palestinian third party who made the same proposal. The results highlight practical problems in mediation where the third party may need the mist not only of the disputing parties but also the trust of nonpartisan others. Evenhanded third party behavior that may impress nonpartisans is likely to he seen as biased mediation by disputants. [ABSTRACT FROM AUTHOR]