To evaluate the role of tissutal carcinoembryonic antigen (CEA) in different types of colonic mucosae specimens from normal, inflammatory and neoplastic tissues were examined in immunofluorescence (IFL) with a monospecific CEA antiserum. Neither the pattern of IFL nor the amount of antigen in the tissue (defined as the antiserum dilution beyond which CEA staining was no longer visible), could reliably distinguish any histological entity a consistent overlap being observed between positive and negative results in malignant and non malignant mucosa. No correlation was found betwen IFL and the level of serum CEA. It is concluded that the tissutal localization of CEA by immunohistochemistry plays no role in the differential diagnosis of different types of colonic mucosa.