The DNA sequence of the white locus of Drosophila melanogaster is presented. This 14,100 base-pair sequence includes the region of the locus required for wild-type levels of expression and control of expression. We also report the sequence of a complementary DNA clone which established the position of the 3' end of the white RNA on this genomic sequence. The probable exon-intron structure of the gene has been predicted from the DNA sequence of the regions known to be represented in the RNA. The amino acid sequence of the protein which would be produced by translation of this RNA suggests that the white locus gene product may be a membrane protein. The DNA sequence rearrangements associated with seven insertion mutants (white-dominant-zeste-like (wDZL), white-spotted (wsp), white-honey (wh), white-zeste-mottled (wzm), white-apricot (wa), white-buff (wbf) and white-hd81b11 (whd81b11)), one deletion mutant (white-spotted 4 (wsp4)) and one internal duplication mutant (white-ivory (wi)) have been determined and positioned on the wild-type sequence. The positions of these insertions and those of previously characterized insertions associated with six other mutations suggest that some insertions within an intron may still allow the production of correctly spliced RNA, but affect the amount, and correspondingly the expression of the w locus.