A 12-kb DNA segment spanning the white+ (w+) locus of Drosophila has been inserted into a P-transposon vector and used for P-factor-mediated germ-line transformation. Several red-eyed transformants were recovered which complement the white mutant phenotype. Analysis of the eye pigments and the interaction with the zeste mutation indicates that the w+ gene inserted at several new chromosomal sites is expressed normally. The tissue-specific accumulation of w+ transcripts, as studied by in situ hybridization to tissue sections, is the same in transformant and wild-type larvae. This indicates that all the genetic information specified by the w+ locus is contained within this 12-kb segment of DNA. By secondary mobilization it was shown that the w+ sequences have been inserted as a functional P(w+) transposon which is capable of further transposition.