Members of the family of carcinoembryonic antigen (CEA)-related cell adhesion molecules (CEACAMs) belonging to the immunoglobulin (Ig) superfamily are expressed in a variety of normal and malignant human tissues. As components of the cell membrane, these glycoproteins can make contact with adjacent cells. CEACAM1 and CEACAM5 (CEA) express Lewis x (Le x) structures. As shown by mass spectrometry in conjunction with enzymatic digestion, CEACAM1 contains at least seven Le x residues. Fucosyltransferase IX is the main fucosyltransferase responsible for attachment of terminal fucose, the key feature of the Le x structure, to CEA and CEACAM1. The Le x residues of both, CEACAM1 and CEA, interact with the human Le x-binding glycan receptors DC-SIGN and SRCL. Since subpopulations of human macrophages express DC-SIGN or SRCL, Le x-carrying CEACAMs may modulate the immune response in normal tissues such as the human placenta or in malignant tumours, for example in colorectal, pancreatic or lung carcinomas.