Following an analysis of the literature, the review concludes that the recent huge increase in our theoretical knowledge of the molecular biology of the CEA family has been accompanied by an adequate practical immunohistological implementation. However, a broader use of CEA as a diagnostic tool has been hampered by variable and conflicting results using poly-clonal anti-CEA antibodies and by lack of standardization of immunohistochemical methods and tissue preparation. CEA immunoreactivity has been demonstrated in a variety of normal and neoplastic tissues, but in all sites with positive staining, at least one other author has failed to identify CEA reactivity. CEA can be used as a marker to identify epithelial differentiation; however, this will be helpful in only 1 % of cases. The introduction of well-defined monoclonal antibodies against clearly defined epitopes of the CEA family will make the differential diagnosis of tumors easier.