Glycodelins are glycoproteins synthesized in various glands, with sequence homology to beta-lactoglobulins, and named according to their unique oligosaccharide structures. We purified, cloned and sequenced endometrium- and seminal plasma-derived glycodelins (GdA and GdS respectively) and found that they are involved in various types of cell-cell communications. These include interactions between the spermatozoon and the egg, and between immune cells and their targets. Endometrial GdA inhibits sperm-egg binding, whereas the differently glycosylated GdS in seminal plasma does not. These observation are of interest for reproductive physiology, detection of causes of infertility, and they also may have potential for contraceptive development.