Self-esteem has been proposed to serve as a sociometer, a gauge of one's value as a relationship partner. Based on evolutionary reasoning, we hypothesized that the sociometer is particularly sensitive to “capacity rejection” in the mating domain. Capacity rejection implies that one has low potential to be an acceptable mate now and in the future. In Study 1, participants received no feedback or negative feedback regarding their capacity for being an acceptable mate or friend. Although participants in both mate and friend conditions felt rejected, only those in the mate condition exhibited significantly lower state self-esteem. In Study 2, we examined sex differences in attributes relevant to mate capacity. Participants were given no feedback or negative feedback regarding their capacity as a mate: Some were told that their low mate capacity is due to their physical attractiveness whereas others were told it is due to their competence and status. Among men, state self-esteem was lower only after competence and status-based rejection; among women, state self-esteem was lower only after physical attractiveness-based rejection. In both studies, additional results revealed that even while self-esteem decreased, positive beliefs about the self were maintained, suggesting that feelings and beliefs about the self react differently to rejection. Copyright © 2009 John Wiley & Sons, Ltd.