'Nomenclature and overview of the mouse (Mus musculus and Mus sp.) immunoglobulin kappa (IGK) Genes', the 19th report of the 'IMGT Locus in Focus' section, provides the first complete list of all the mouse (M. musculus) IGK genes. The mouse (M. musculus) locus spans 3,200 kb. The total number of mouse (M. musculus) IGK genes per haploid genome is 164 (174 if the orphons are included). The functional genomic repertoire comprises 93 IGKV belonging to 18 subgroups, 5 IGKJ and 1 IGKC gene. IMGT gene names and definitions of the mouse (M. musculus) IGK genes on chromosome 6 and IGK orphons are provided with the gene functionality and the number of alleles, according to the concepts of IMGT-ONTOLOGY and to rules of the IMGT Scientific chart, with the accession numbers of the IMGT reference sequences. These tables and figures are available at the IMGT Marie-Paule page of IMGT, the international ImMunoGeneTics database (http://imgt.cines.fr) created by Marie-Paule Lefranc, Université Montpellier II, CNRS, France. Copyright 2002 S. Karger AG, Basel