The shortage of human tissues for allografts has led physicians to consider swine tissues and organs as a possible substitute. Recent success in overcoming the hyperacute rejection phase of porcine tissues in non-concordant xenotransplantation experiments support their possible use for human transplantation even though formidable obstacles remain. Among the antigenic determinants present in porcine cells, molecules of the major histocompatibility complex (MHC) play a pivotal role. Further manipulation of the swine MHC requires the sequence of the corresponding chromosomal fragment. A first BAC clone is now being sequenced. It comprises at least 7 class I loci including classical genes.