Abstracts of Poster Sessions

NUMEROUS antigens have been described to date that were claimed to crossreact with the carcinoembryonic antigen of the digestive tract (CEA) discovered by Gold and Freedman (1965). Among them, only one has been sufficiently purified and characterized to allow further, more detailed studies of its immunological relationship with CEA, its identity with other cross-reacting substances, and its possible clinical value. This antigen has been given 4 different names. NCA (for " non-specific crossreacting antigen ") is our name for it (von Kleist, Chavanel and Burtin, 1972) and other names are NGP (for " normal glycoprotein ") favoured by Mach and Pusztaszeri (1972), CCA III by Newman et al., (1972) and CE-X by Darcy, Turberville and James (1973), who showed the immunological identity of 3 of these antigens (NCA, NGP and CE-X). NCA is one of the 3 principal colonic carcinoma antigens regularly present in perchloric-acid extracts of these and other tumours and normal tissues, and a tenacious contaminant of CEA preparations (von Kleist et al., 1972; von Kleist, 1973). There exist many physico-chemical similarities between the two antigens; they differ from each other, however, in molecular weight and by the unshared antigenic determinants on their respective molecules. This permits their separation and specific detection in tissues and body fluids. Accepted 14 February 1977