The present study simulated an organizational dispute to test two sets of alternative hypotheses regarding the effects of within-group cooperation and conflict on a subsequent negotiation with an out-group. The first set of hypotheses concerned in-group cooperation. We expected that either (a) in-group cooperation would produce greater cooperation toward an out-group, the result of a carryover effect; or (b) in-group cooperation would increase group cohesiveness and strengthen group boundaries, and thus produce greater competitiveness toward an out-group. The second set of alternative hypotheses concerned in-group conflict. We expected that either (a) in-group conflict would produce greater competitiveness toward an out-group, the result of a carry-over effect; or (b) in-group conflict would decrease group cohesiveness and weaken group boundaries, and thus produce less competitiveness toward an out-group. Subjects in three-person groups negotiated first with one another on a cooperative or competitive task, and then as a group, with another group. The data supported the carryover hypothesis for the effects of both in-group cooperation and conflict. Groups that experienced internal cooperation were more cooperative in the subsequent between-group negotiation and, to a lesser extent, groups that experienced internal conflict were more competitive in the subsequent between-group negotiation, relative to a control condition that had no prior in-group negotiation. Taken together, the results were consistent with recent research on dispute intervention that suggested that mediators in between-group conflict should foster within-group cooperation prior to between-group negotiations.