Abstract: Four specimens of colon-rectal carcinomas were stained histochemically and immunochemically using horseradish peroxidase labeled anti-CEA Fab antibody for the detection of CEA tumor marker, The results proved that Fab antibody fragment labeled with horseradish peroxidase better penetrated into the tissue owing to its smaller molecular weight, In addition, this method is simple, reliable and may be used for the detection of gastrointestinal adenocarcinomas as auxiliary procedure for pathological diagnosis.

Key words: horseradish peroxidase, antibody against CEA, immunohistochemical staining) tunot's market CEA, colon-tectal carcinoma