Glycodelins are 28 to 30-kD glycoproteins synthesized in various glands, notably those of the male and female reproductive organs. Depending on the site of origin, the same protein backbone is glycosylated in different ways, yielding glycodelins with different biological actions. Thus, human endometrium-derived glycodelin-A is temporally expressed in the latter half of the menstrual cycle, consists of unique sialylated and fucosylated lacdiNAc oligosaccharide sequences, and inhibits sperm-egg binding. By contrast, glycodelin-S from seminal vesicles has no such oligosaccharide sequences and no contraceptive activity. Glycodelin-A also has potent immunosuppressive properties, and its chemically modified forms inhibit transmission of HIV in vitro. Studies are reviewed suggesting that glycoforms dictate the function of human glycodelins, and that some of the oligosaccharide recognition sites present in the human gametes and immune cells have converged.