In line with the challenge hypothesis, this study investigated the effects of the presence of a woman on the testosterone (T) levels of young men. An informal contact with a woman of approximately 5 min resulted in an increase in salivary T among men. These effects occurred particularly in men with an aggressive dominant personality. In addition, higher salivary T levels were related to a more aggressively dominant personality, being sexual inactive for a month or more, and not being involved in a committed, romantic relationship. The most important findings of this study are that the short presence of a woman induces specific hormonal reactions in men, and that these effects are stronger for aggressively dominant men.