The past year has seen several advances in the analysis of the HLA class I region and some of its resident genes. A description of the human class I gene family and the cloning of the class I region in yeast artificial chromosomes have provided two steps forward in the analysis of the class I region. Advances have been made in understanding the expression of the non-classical HLA class Ib genes and work with the murine class Ib proteins has demonstrated that these antigens can present a specialized subset of peptides to the immune system.