The physical maps of three cloned D. melanogaster DNA fragments with genes for the 70,000 dalton heat-shock protein (hsp 70) are presented. Fragment 122 contains two genes in diverging orientation, forming an inverted repeat around a central spacer. The other two fragments, which are found as polymorphic variants in the fly population, have related structures; they differ by the deletion or the insertion of large DNA segments. The sequence homologies between 122 and a plasmid with two hsp 70 genes in tandem repetition was investigated by heteroduplex analysis. In addition to the basic gene units, the segments share other homologous sequence elements which are found in different combinations near the beginning of the genes.