The carcinoembryonic antigen (CEA) gene family consists of approximately 30 genes, of which 17 are transcriptionally active. These genes are tightly clustered on the long arm of chromosome 19. Two main subgroups are distinguishable, one encoding CEA and its classical non-specific cross-reacting antigens (NCAs) and the second encoding the pregnancy-specific glycoproteins (PSGs). The CEA family belongs to the immunoglobulin superfamily. CEA subgroup members are either membrane bound through a glycosyl phosphatidylinositol anchor, or are integral membrane proteins, whereas PSG molecules are secreted from the cell. Despite high sequence similarity, CEA family members reveal variable expression patterns, indicating different functions. Apart from its high expression in various adenocarcinomas, CEA is found in epithelia lining the gastrointestinal tract, in eccrine sweat glands, lung epithelia and testes. The NCAs are often coexpressed with CEA, but are also found in granulocytes. PSGs are coexpressed in syncytiotrophoblast cells of the placenta, submandibular salivary glands and fetal liver, as well as in choriocarcinomas and breast tumours.