Members of the carcinoembryonic antigen (CEA) family include CEA, non-specific cross reacting antigen (NCA), and bthary glycoprotem (BGP). and appear to function as cell adhesion molecules. Immunoprecipitation and subsequent gel electrophoresis of proteins from several colon cancer cell lines labeled with [y-3ZP]ATP, under conditions designed to detect ecto-kinase-catalyzed phosphorylation of cellular proteins, revealed that polyclonal anti-CEA antiserum recognized a 175-190 kDa phosphoprotein on the surface of colon cancer cells. The ability to detect this phosphoprotein did not correlate with CEA production, and immunoprecipitation studies suggested that the phosphoprotein is BGP. Phosphoamino acid analysis of the 175-190 kDa protein showed that it contained predominantly phosphotyrosine.