This study concerns the immunohistologic distribution of carcino-embryonic antigen (CEA) in tissues and organs from 86 legal abortions, stillborn fetuses and perinatal deaths and from 5 adults without inflammatory disease or cancer. Monospecific antibodies to CEA of both polyclonal and monoclonal origin were applied to serial sections obtained from formalin-fixed, paraffin-embedded tissue blocks. Starting from the 9th week of gesta-tional age, a positive staining reaction for CEA was found in the surface epithelium of the tongue, the tracheal mucosa and the following locations of the gastro-intestinal tract: the gastro-oesophageal junction, the pyloric antrum, the upper duodenum, throughout the colon and appendix. In the adult, CEA was also found at these sites. All other organs such as the central nervous system, lung, thyroid, thymus, liver, pancreas, gastric corpus, spleen, adrenals, kidney, ureter, bladder, gonads and breast were negative for CEA. Therefore, CEA appears to be a normal antigen in the gastro-intestinal tract at any age from fetal life onwards.