Abstract The DNA of Drosophila virilis contains three highly repetitive density satellites that constitute approximately half the genome. Complementary RNA was synthesized enzymatically from the separated strands of the purified satellite DNAs. By sequencing the transcripts we have shown that the satellites are repeating heptanucleotides related to each other by simple base-pair changes. The sequences are: I, poly d(A-C-A-A-A-C-T): poly d(A-G-T-T-T-G-T); II, poly d(A-T-A-A-A-C-T): poly d(A-G-T-T-T-A-T); III, poly d(A-C-A-A-A-T-T): poly d(A-A-T-T-T-G-T). Thus, despite different physical properties (buoyant density and T m ), the three satellite DNAs of this species constitute a family of related sequences. The major satellite in another species, D. americana americana, was shown to be identical to satellite I of D. virilis. The evolution of satellite DNAs in Drosophila requires a mechanism that maintains homogeneity of repeated sequences over many thousands of generations while permitting the origin of new satellites with single base-pair changes in each repeating unit.