IMGT, the international ImMunoGeneTics database((R)) (http://imgt.cines.fr), is a high-quality integrated information system specializing in immunoglobulins (IG), T cell receptors (TR) and major histocompatibility complex (MHC) of human and other vertebrates, created in 1989, by LIGM, at the Université Montpellier II, CNRS, Montpellier, France. IMGT provides a common access to standardized data which include nucleotide and protein sequences, oligonucleotide primers, gene maps, genetic polymorphisms, specificities, 2D and 3D structures. IMGT includes several databases (IMGT/LIGM-DB, IMGT/3Dstructure-DB, IMGT/HLA-DB), Web resources ('IMGT Marie-Paule page') and interactive tools (IMGT/V-QUEST, IMGT/JunctionAnalysis). IMGT expertly annotated data and tools described in this paper are particularly useful for the analysis of the IG and TR rearrangements in leukemia, lymphoma and myeloma, and in translocations involving the antigen receptor loci. IMGT is freely available at http://imgt.cines.fr.