The Ca(2+)-independent homotypic and heterotypic cell adhesion activities of a carcinoembryonic antigen (CEA) family member, W272 (CGM6), whose cDNA has recently been isolated from libraries of human peripheral leukocytes of apparently normal subjects (Arakawa, F., Kuroki, Mo., Misumi, Y., Oikawa, S., Nakazato, H., and Matsuoka, Y. (1990) Biochem. Biophys. Res. Commun. 166, 1063-1071) and spleen of chronic myelogenous leukemia patients (Berling, B., Kolbinger, F., Grunert, F., Thompson, J. A., Brombacher, F., Buchegger, F., von Kleist, S., and Zimmermann, W. (1990) Cancer Res. 50, 6534-6539) has been examined. Chinese hamster ovary cells transfected with the cDNA for W272, CEA, nonspecific cross-reacting antigen (NCA), and various antigens containing chimeric N-domain have been used. The W272 producers did not show homotypic binding at all but bound only to the cells expressing NCA and a chimeric CEA whose N-domain is substituted by that of NCA, indicating the major contribution of N-domain of NCA in the specific binding. The importance of the N-terminal region of NCA N-domain for the W272-NCA binding has been shown by detailed analysis using COS-1 cells producing various NCA whose N-domain are chimera of that of NCA and CEA. The strict heterotypic nature of the W272-NCA adhesion strongly suggests that the cell adhesion activities exhibited by CEA family members are not the fortuitous activity but the specific one which have some important physiological roles.