CEA-like molecules immunologically distinct from those in humans have been described in non-human primates. These primates do not share the human predilection for colitis and subsequent development of colorectal cancer. CEA expression has not been fully evaluated in a lower-order primate, the cotton-top tamarin (Saguinus oedipus), an animal model for colitis and colorectal cancer. We found increased levels of CEA in both colonic washings and tissues of these animals using a commercially available kit, CEA AIA-PACK (Tosoh Medics, Foster City, CA). In contrast, we observed that other CEA kits failed to detect CEA in tamarins. To elucidate the nature of the CEA-like protein detected, we used the two component monoclonal antibodies used in the CEA AIA-PACK kit, and identified the reactive molecules by Western blotting. A band of approximately M(r) 50,000 was found to be common to samples from both humans and the tamarins. Minimal binding was observed with NCA antibody. We conclude that a CEA-like molecule shared by humans and tamarins may play a role in the pathogenesis of colitis and cancer in both species.