Department of Psychology, University of Texas, Austin, TX 78712-0187, USA.

The ovarian steroid hormone oestradiol plays a crucial role in female fertility, sexual motivation and behaviour. We investigated the relationship between oestradiol and the likelihood that women would engage in opportunistic mating. Two salivary samples were taken from normally cycling women within the peri-ovulatory and luteal phase of the menstrual cycle. At both testing sessions, participants also completed self-perceived desirability scales and provided subjective reports of sexual and social motivations, and satisfaction with their primary relationship partner. Oestradiol level was positively associated with a woman's self- and other-perceived physical attractiveness and with inclinations to mate outside her current relationship. Oestradiol was marginally negatively associated with a woman's satisfaction with her primary partner and relationship commitment. Results provide support for the relationship between physical beauty and fertility and suggest that physiological mechanisms play a major role in guiding a woman's mating strategies.