We describe the molecular identification of a gene, designated T1, whose expression in mouse NIH 3T3 cells is strongly induced by the Ha-ras(EJ) and v-mos oncogenes and by serum. The T1 gene encodes a 38.5-kDa protein, as predicted from its primary sequence and shown by in vitro translation. The protein was processed at its amino terminus and extensively modified by N-linked glycosylation in vitro in the presence of microsomal vesicles. Sequence comparison of T1 with the MIPSX data base (Max-Planck-Institut für Biochemie, Martinsried/Munich) revealed similarity to the human carcinoembryonic antigen, a tumor marker which is overexpressed in colon adenocarcinomas and in fetal tissues. Considerable sequence similarity has also been observed to the short conserved region of other proteins which, like carcinoembryonic antigen, are encoded by members of the immunoglobulin gene superfamily.