The sequence of mature human CEACAM1 N-domain was aligned with the corresponding domain of murine CEACAM1, giving a gapless alignment for residues 1-109 with a residue identity of 42%. The crystal structure co-ordinates of mouse CEACAM1 (residues 1-109) were taken from the structure file containing domains 1 and 2 (PDB code 1L6Z) and a homology model of human CEACAM1 N-domain was built using standard methods. Final refinement of the model was performed by soaking it with a 5 Å thick layer of water and energy minimizing while constraining the backbone atoms to their original positions in the template structure. The final round of minimization was for 2000 conjugate-gradient steps, constraining the backbone heavy atoms with a force constant of 0.5 kcal/Å. A stereochemical analysis of the structure was performed using Procheck and found to be of similar quality to the template crystal structure.