Estrogen and progesterone induce characteristic and predictable morphological changes in the endometrium that are required for successful implantation and pregnancy. The mechanism(s) by which estrogen and progesterone exert these effects on the endometrium is not known. We propose to identify genes that are induced by endogenous estrogen and progesterone using in situ hybridization, immunohistochemistry, and culture of human endometrium obtained at hormonally different times of the cycle. Regularly cycling women not at risk for pregnancy will be studied for two menstrual cycles. The first, pre-biopsy cycle, will be characterized by daily basal body temperature measurements and a luteal phase progesterone measurement. During the biopsy cycle, urinary LH measurements will be performed to determine the day of the LH surge. Ovarian ultrasounds to assess follicular development will be performed before biopsy. Blood will be obtained on the day of the biopsy to characterize the hormonal mileau. An endometrial biopsy will be obtained either in the early follicular phase (at a follicular diameter of less than 8 mm), the late follicular phase (follicular diameter greater than 14 mm) or in the mid-(luteal phase day 6-8) or late (luteal phase day 12 - 14) luteal phase, to allow identification of endometrial products under conditions of estrogen, estrogen/progesterone and steroid withdrawal. Alternatively, endometrial tissue may be obtained from normal women and those with endometriosis at the time of menses using a cup-shaped intravaginal collecting device. Additionally, women with infertility possibly related to endometrial dysfunction will be studied in the luteal phase.