Two forms of competitive encounters namely Randori (free fight) and Kata (highly ritualized fight) were studied in 22 professional male judo fighters. The dyadic, symmetrical (in terms of body weight and fighting ability) encounters were videotaped to assess relationships between agonistic behavior and individual variations in plasma levels of testosterone (T), cortisol (C) and interleukins (IL-6 and IL-1β) measured before and after the competition. Unremarkably, winners showed longer attack but devoted less time to defensive behaviors when compared to losers. T increased only during Randori but the individual pre- and post-competition T levels recorded in such fights were strongly correlated with the corresponding measures in the Kata for the same individuals. Interestingly, the pre- and post-Randori competition T levels were higher in losers than in winners and T variations positively correlated with the frequencies of attacks and with the duration of defensive postures. The T response shows individual variation and seems to reflect evaluation of the likelihood of winning or losing. Both Randori and Kata induced a marked C increase, although the pre- and post-Randori hormonal titers were higher than those found for the Kata. IL-6 significantly increased between the pre- and the post-Randori competition, but no such changes occurred during the Kata. No correlations were found between individual pre- and post-competition C and IL-6 and IL-1β levels in either Randori or Kata. This suggests that C and cytokine release are unrelated to emotional or cognitive perception of the possible outcome of fighting but are a consequence of general motor activity. Martial arts appear to provide good human models to understand: (a) the relationships between conflict, hormones and the immune system and (b) the relationships between mood and physiological responses to competitive aggression. Aggr. Behav. 32:1–9, 2006. © 2006 Wiley-Liss, Inc.