DNAs from inbred rat strains representing eighteen major histocompatibility complex (RT1) haplotypes have been tested for restriction fragment length polymorphisms of the three heat shock protein 70 (Hsp70) genes mapping into this complex. The DNAs were digested with restriction enzymes BamHI, EcoRI, PstI or PvuII and assayed by probes hybridizing to all three genes or selectively to Hsp70-1, Hsp70-2 and Hsp70-3, respectively. Three to four alleles were detected with each enzyme and in total five different strain distribution patterns could be found. Neither deletions nor amplifications of genes were detected in the three-gene Hsp70 cluster.