The inhibitors ofNF-B (IBs) play an important role in the regulation of the NF-B pathway. IBR (for IB-Related) is proposed to be a novel member of this family. We report the cloning and characterization of the region of the human gene encoding the previously reported mRNA. This region contains 13 exons, spread over 6550 bp of genomic sequence. The coding sequence is only weakly similar to other IBs and the exons display a more complicated structure than has been found in other members of the IB gene family. Moreover, the positions of intron-exon junctions are different from those found in other IB genes, even within the otherwise conserved ankyrin-like repeat region, suggesting that the IBR gene is not a member of this extended gene family. We report a revised mRNA and protein sequence for IBR, which predicts that the protein is larger than originally described. We also report the chromosomal localisation of the human IBR gene (approved gene symbol NFKBIL2) to 8q24.3 using PCR-based somatic cell hybrid panel analysis and fluorescence in situ hybridization (FISH) mapping.