The organization of the three major histocompatibility complex (Mhc)-linked heat shock protein 70 (Hsp70) genes Hsp70-1, Hsp70-2, and Hsp70-3, and the nucleotide sequences of these genes, are presented for the rat. Hsp70-1 and Hsp70-2 gene products are identical at the amino acid level. From the pattern of sequence similarity of the orthologous Mhc-linked Hsp70 genes of rat, human, and mouse, it is concluded that the gene duplications leading to the three-gene cluster occurred before the separation of the primate and rodent lines and that the Hsp70-1 and Hsp70-2 genes of rat and human might have undergone homogenization of their sequences.