In an effort to identify all CEA gene family members in the dog genome we employed the BLAST program to search the GenBank and Ensemble databases (CanFam 1.0, July 2004) using cDNA nucleotide sequences from all known human and mouse CEA family members as query sequences. The human and mouse CEA gene families are located within the expanded leukocyte receptor complex on chromosome 19q13 ( Figure 1A ) and chromosome 7, respectively. This approach yielded the sequences of the CEACAM1, CEACAM16, CEACAM18, CEACAM19 and CEACAM20 orthologs. Their predicted full length mRNA sequences (Additional file 1) encode proteins with domain organizations identical with their human and murine counterparts: CEACAM16 (N1-A-B-N2); CEACAM18 (N-A-B-TM-Cyt); CEACAM19 (N-TM-Cyt); CEACAM20 (truncated N-A1-B1-A2-B2-TM-Cyt) [3] . Like their mouse and human counterparts, both CEACAM19 and CEACAM20 contain presumed ITAM consensus sequences in their cytoplasmic domains. However, like in mouse, no CEACAM19 cytoplasmic domain exon 1 present in human CEACAM19 was found [3] . As for human CEACAM18, no cytoplasmic domain exon could be identified due to its small size and lack of corresponding EST sequences. In a second round of search we used the BLAST program and cDNA nucleotide sequences from the identified orthologous canine genes to screen the Gen-Bank and Ensemble databases. This strategy was employed in order to identify dog-specific genes which have evolved after the separation of the dog and primate/ rodent lineage. This approach led to the identification of 7 additional CEACAM genes (CEACAM23-CEACAM29) using CEACAM1 nucleotide sequences as query sequences. CEACAM23, CEACAM24, CEACAM25, CEACAM29, CEACAM28 and CEACAM1 are arranged between XRCC1 and LIPE, while CEACAM26 and CEACAM27 are located between CD79A and TGFβ1 on the opposite strand ( Figure 1) . Surprisingly, no genes corresponding to the PSG genes were found. The murine Psg genes are located between Hif3a and Pglyrp1 spanning nearly 1.8 Mbp. In dog, however, the distance between HIF3A and PGLYRP1 comprises only 0.1 Mbp which rules out the presence of a larger set of genes between these marker genes. Similarly, there is not enough space between XRCC1 and CEACAM23 (0.2 Mbp) to accommodate an expanded PSG gene family as found in humans at the corresponding chromosomal locations location where the distance is approximately 1 Mbp ( Figure 1B) . The canine CEACAM gene loci on dog chromosome 1 exhibit a similar arrangement to that found for the human CEA gene family on chromosome 19 but it is partially different from that of the murine CEA gene family on chromosome 7 ( Figure 1B) .