Abstract The genome of a Drosophila hydei genotype with a reduced amount of heterochromatin was fractionated by three cycles of preparative gradients: firstly in Ag +/Cs 2SO 4, secondly in actimomycin D/CsCl, and finally in neutral CsCl. Using this method, twelve highly repetitive simple-sequence satellites were isolated. Ten of them comprised only a minor amount of the genome in contrast to the two major satellites found earlier 1 ( p = 1.696 and 1,714 g/cm 3). These minor satellites were characterized by their banding in the gradient systems used, by their density in neutral CsCl, and by their melting point. Using these characteristics, it was found that the fractions of the Ag −/Cs 2SO 4 gradient do not contain purified single components, because up to five different satellites band in the same position of the Ag −/Cs 2SO 4 gradient. It was possible to isolate a high number of satellites even from a genome with a reduced amount of heterochromatin. Thus, the D hydei heterochromatin does not domain one unique highly repetitive sequence DNA, but is comprised of many different satellite sequences.