Using the method of P-element-mediated enhancer detection, 29 Drosophila melanogaster lines were obtained that carried P-1ArB vector insertions in chromosomes 2 and 3. The expression of the reporter gene lacZ at different developmental stages of the transformed lines was determined in color reactions for beta-galactosidase. Regions of vector integration were located using in situ hybridization. Subsequent electron-microscopic mapping of the transformed regions was performed using four lines (nos. 12, 41, 2, and 3). In the lines 12 and 41, lacZ was expressed in most tissues of embryos, larvae, and imagoes (including salivary glands), whereas in lines 2 and 3 its expression was observed only in embryos. Lines 12 and 2 showed the presence of insertions in the 85D9/10 and 86B4/6 interband regions, respectively. The absence of a novel band in line 3 could be associated with transposon integration into the band. In line 41, puffing of the transformed region was observed, which did not allow us to determine the presence of any novel structures in it. The novel structures in lines 12 and 2 looked like single bands with a similar DNA packing ratio of about 30. These bands were obviously polygenic, because the inserted vector contained four functionally different genes.