The vestigial gene (vg+) is required for normal wing development and is expressed in a spatially distinct pattern in imaginal discs. We have exploited a general property of P element alleles to target an enhancer trap to the 5' region of the gene. By replacing the P element resident at this site in vg21 with a P element carrying a lacZ reporter gene, the vglacZ1 allele was selected on the basis of its increased mutant phenotype. In contrast to vg+ expression, which occurs primarily in the presumptive wing margin and hinge, beta-galactosidase expression in vglacZ1 wing discs is localized to the dorsal wing surface and displays homologous haltere expression. The targeting of P element enhancer traps could be readily extended to other genes with low rates of primary P element insertion.