Immunoperoxidase staining allows detection of small amounts of antigens in tissues, and can be applied to formalin-fixed, paraffin-embedded specimens several years old. We utilized this technique to stain for carcinoembryonic antigen (CEA) in 11 specimens of colon from 10 patients with ulceratve colitis. We compared the degree of epithelial abnormality in these mucosal specimens with the extent of immunoperoxidase staining for CEA. CEA staining was also comapared with the duration of colitis, extent of colonie in volvement, the indication for colectory, and the medical therapy before colectomy. We found that neither cytoplasmic nor cell surface CEA staining correlated with the degree of epithelial alteration. Similarly, CEA staining did not correlate with any of the clinical parameters evaluated. We conclude that immunoperoxidase staining for CEA is not useful in assessing the degree of dysplasia in mucosal specimens from patients with ulcerative colitis. There seems to be no clinically relevant role for anti-CEA staining in ul-cerative colitis.