The desire for positive social relationships is a fundamental motive shaping human cognition and behavior. In the current research, I integrate social cognitive, evolutionary, and neuroendocrinological theories to generate and test predictions about how female affiliative motives shift naturally across women's menstrual cycles and how these shifts relate to functional changes in attention. Consistent with a social monitoring system hypothesis, during the luteal phase of their cycle, normally cycling women, but not women on oral contraceptives, displayed greater attentional attunement to social stimuli than non-social stimuli. Moreover, attention to social stimuli was associated with normally cycling women's levels of progesterone – a hormone closely tied to affiliative motivation. The current research suggests that endocrinological mechanisms are functionally linked with lower-order cognitive processes designed to help foster positive social relationships.