A complementary DNA clone encoding the ADP/ATP translocase in Drosophila melanogaster has been identified. It has been shown by sequence analysis to contain a single open reading frame that encodes a polypeptide 297 amino acids long. This polypeptide shows extensive similarities to the known eukaryotic translocase polypeptides, the similarity being greatest (up to 80% identity) to the mammalian ADP/ATP translocases. In situ hybridization to polytene chromosomes of D. melanogaster with the sequence characterized in this study showed localization at a single site on the X chromosome at 9E. DNA transfer hybridization experiments suggest that more than one gene coding for the ADP/ATP translocase is present in the D. melanogaster genome.