Although most of the literature suggests that females are more cooperative than males, research on the Prisoner's Dilemma (PD) game has often found females more competitive. Analysis of the PD game suggests that the term "cooperation" has been used differently in that context than in other situations. Cooperation usually refers to a style of behavior characterized by fairness, equalit}', and sharing, while in the PD game it refers to one of two alternative choices. Other past research has indicated that males are primarily motivated to win in a competitive situation, while females are more concerned with interpersonal accommodation. Combining these two lines of research, it was predicted males'vvould make choices in the PD game in such a way as to maximize their winnings, while females would alter their choices on the basis of the social nature of the setting. Two PD game studies were undertaken in which, for half of the subjects, the cooperative response would lead to higher winnings, while for the remaining subjects the competitive choice was optimal. In the first study 40 subjects played with like-sex partners, while in the second study 80 subjects played with opposite-sex partners, whose physical attractiveness varied. Both studies found males more likely than females to make the optimal choice, while females were more likely to vary their choices as a function of the sex and attractiveness of their partner. The findings suggest that males and females do not have differential motives to cooperate, but respond to different cues.