A three-dimensional model of CEACAM1 N-domain was previously produced based on the Ig family molecules REI, CD2 and CD4 (Fig. 1A ) (Virji et al., 1999) . In this model, whilst most mutations affecting binding of Nm and Hi were located centrally on the CFG face of the protein, Val-39 involved in Opa binding, was located at a distance towards the bottom of the CFG face (Fig. 1A) . Subsequently, a crystal structure of murine soluble CEACAM1a domains 1 and 4 was reported (Tan et al., 2002) . Based on this, we have remodelled the human CEACAM1 Ndomain. The CC′ loop that contains Val-39 folds back against the CFG face of this model such that it lies in close proximity to the other critical residues involved in bacterial adhesion (Fig. 1B) . Further examination of this model suggested that the bacterial binding pocket forms a rather flat surface in the centre of the CFG face. It also appears that substituting neighbouring residues Tyr-34 and Gln-89 by Phe and Asn, respectively, could result in a further flattening of the bacterial binding surface (Fig. 1C-E) , providing increased access to the key Ile-91. These residue changes also increase the size of the hydrophobic patch centred on I91 (Fig. 1C-E) . Both of these effects might facilitate binding of some bacterial ligands to the target receptor.