The consistently better performance seen by teams in various sporting contexts when playing at home is referred to as the ‘home advantage’. Various explanations have been put forward to account for this robust phenomenon, though none has yet focussed on possible hormonal factors. In an initial study, we showed that salivary testosterone levels in soccer players were significantly higher before a home game than an away game. In a second study involving a different group of soccer players, this finding was replicated over two home games, two away games, and three training sessions. Perceived rivalry of the opposing team was important as testosterone levels were higher before playing an ‘extreme’ rival than a ‘moderate’ rival. Self-reported measures of mood in both studies were not linked to testosterone level. The present results corroborate and extend earlier findings on the relationships between testosterone, territoriality, and dominance in human competitive encounters and further suggest an important role for testosterone in the home advantage seen in various team sports.