P-element mediated transformation was utilized to introduce a suppressor tRNA gene (Sup3e tRNA(UGASER)) from Schizosaccharomyces pombe into Drosophila melanogaster. Thirteen independently transformed lines were characterized as to the number of cytological locations of the transposons. It was ascertained that the suppressor tRNA gene of interest was introduced into each transformed strain. The helper P element used (p pi 25.1) allows further transposition to occur, and it was determined that from one to seven copies of the heterologous tRNA(UGASER) gene per strain were present among the respective transformed strains. The number of transposons per transformed line was established by in situ hybridization to salivary gland chromosomes as well as by Southern hybridization analyses and there was good agreement in the totals determined by these two techniques.