Testosterone concentrations change rapidly in the context of athletic competition (Archer, 2006). Also, simply watching one's team compete has similar effects on testosterone concentrations (CarrÃ© & Putnam, 2010). Despite these findings, there remains widespread variation in testosterone responses to competitive interactions. One potential factor that may underlie such variability is an athlete's social identity - identity formed through membership on a team. The purpose of this study was to examine the relationship between social identity and testosterone responses in male combative sports athletes' watching video footage of their teammate competing (win/loss). Male combative sport athletes (n=28, Mage = 29.43, SD=1.11) completed a questionnaire assessing three dimensions of social identity (ingroup ties, cognitive centrality, and ingroup affect) and provided saliva samples before and after watching video footage of teammates competing. Multiple regression analysis indicated that perceptions of ingroup ties moderated the relationship between competition outcome and testosterone response, F(1,20)=6.00, p=.02. Simple slopes analyses revealed that athletes who identified strongly with their team and teammates had an increase in testosterone when watching a teammate win, and a decrease in testosterone when watching a teammate lose. However, the opposite pattern of neuroendocrine response was observed in athletes who had low identification with their team. Specifically, a decrease in testosterone was observed when watching a teammate win, and an increase in testosterone was observed when watching a teammate lose. These findings indicate that social identity may play a salient role in moderating one's testosterone response when watching their teammates in a competitive performance.