This dissertation project investigated fluctuations in estradiol and testosterone across the human menstrual cycle. During the part of the cycle when women are most fertile, women show stronger preferences for men with more masculine faces, and these preference changes may be related to changes in hormone levels during ovulation. The present study investigated preferences changes among women for higher testosterone men over the menstrual cycle as estradiol and testosterone in those women fluctuated. 32 women participated in this 5-week long study tracking their estradiol and testosterone levels and preferences for masculine men. Women with higher levels of estradiol preferred men who had higher levels of testosterone than women who had lower levels of estradiol. During ovulation, women were more like to find high testosterone men more attractive than other parts of the menstrual cycle. In addition to ratings of men, several other psychological tests were administered and examined for changes as a function of state and trait levels of hormones.