The longitudinal expression of endometrial epidermal growth factor receptor (EGF-R) mRNA throughout the menstrual cycle will be studied. Each patient will have five endometrial biopsies and serum hormone analysis performed within two menstrual cycles. Reverse transcriptase polymerase chain reaction will be used to semiquantitatively determine the relative amount of mRNA for EGF-R. To study the production of a special protein in the lining of the uterus and evaluate the relationship of this protein to normal changes in the endometrium.