Major histocompatibility complex (MHC) class I molecules mainly resent antigenic peptides derived from cytosolic and nucleic proteins. The discovery of four new genes, namely Tap1, Tap2, Lmp2, and Lmp7, in the human, mouse, and rat MHC class II regions has shed light on the mechanisms repsonsible for the production and transport of these antigenic peptides for presentation by MHC class I molecules. Little is known about the polymorphism of LMP2 and LMP7 molecules. We have shown previously that three amino acid variants of LMP2 are distributed among 12 inbred mouse strains. Here, we have extended this analysis by sequencing the Lmp7 gene in different strains of mice. Altogether, our studies provide a clear insight into the distribution of LMP2 and LMP7 alleles among mouse haplotypes. 20 refs., 1 fig., 3 tabs.