2. To identify the surface molecules on EEC responsible for attaching to BAP-EB. The biotin-labeled primary EEC surface proteins that bind onto BAP-EB will be purified and identified by mass spectrometry. The bound proteins from "receptive" and "non-receptive" endometrial cell lines will be compared. The expression of the surface proteins on endometrial samples obtained in Objective 1will be correlated with their BAP-EB attachment rate.