Internationalist and isolationist Ss played a 2-part modification of the Prisoner's-Dilemma-type game. Though they did not know it, they were actually playing against E, rather than each other. In the 1st part of the experiment, Ss had little control over the payoff matrix. In the 2nd part, Ss had virtually total control over the payoffs. During the 1st part of the experiment, E played a "cooperative" strategy against ½ of the Ss and a "competitive" strategy against the other ½. The results indicated that neither the strategy played against Ss nor the personality of Ss influenced the number of cooperative choices. However, a significant 3-way interaction indicated that internationalists are more sensitive to changes in their opponents' strategies. (PsycINFO Database Record (c) 2016 APA, all rights reserved)