In two experiments, male college students either won or lost $5 on a task controlled entirely by chance. In both studies, winners reported a more positive mood change than did losers and, in Experiment 2, winners reported a more positive mood change than a neutral group that did not win or lose money. After the task was completed, winners exhibited significantly higher testosterone levels than losers. Levels of cortisol, a hormone associated with stress and arousal, did not differ among the groups, suggesting that a hormone-behavior response pattern for winning and losing is specific to testosterone. These data suggest that winning can alter testosterone levels in men and that mood may mediate such changes.