Fragments from the 3B-3C region of the Drosophila X chromosomes were microdissected from salivary gland squashes and their DNA was cloned by the method developed by Scalenghe et al. (1981). These clones were used as starting points for a chromosome walk which covers 200 kb including bands 3B2 to 3C2. A number of deletion breakpoints were mapped on the cloned DNA allowing the localisation of several genes in the 3B region. The white locus in particular was isolated by microcloning the w insertion site. Two transcripts, of 2 and 2.4 kb, respectively, arise from the white region and its vicinity.