We describe the isolation of a cloned DNA segment carrying unique sequences from the white locus of Drosophila melanogaster. Sequences within the cloned segment are shown to hybridize in situ to the white locus region on the polytene chromosomes of both wild-type strains and strains carrying chromosomal rearrangements whose breakpoints bracket the white locus. We further show that two small deficiency mutations, deleting white locus genetic elements but not those of complementation groups contiguous to white, delete the genomic sequences corresponding to a portion of the cloned segment. The strategy we have employed to isolate this cloned segment exploits the existence of an allele at the white locus containing a copy of a previously cloned transposable, reiterated DNA sequence element. We describe a simple, rapid method for retrieving cloned segments carrying a copy of the transposable element together with contiguous sequences corresponding to this allele. The strategy described is potentially general and we discuss its application to the cloning of the DNA sequences of other genes in Drosophila, including those identified only by genetic analysis and for which no RNA product is known.