Mitochondria are organelles present in the cytoplasm of most eukaryotic cells; although they have their own DNA, the majority of the proteins necessary for a functional mitochondrion are coded by the nuclear DNA and only after transcription and translation they are imported in the mitochondrion as proteins. The primary role of the mitochondrion is electron transport and oxidative phosphorylation. Although it has been studied for a long time, the interest of researchers in mitochondria is still alive thanks to the discovery of mitochondrial role in apoptosis, aging and cancer. Aim of the MitoDrome database is to annotate the Drosophila melanogaster nuclear genes coding for mitochondrial proteins in order to contribute to the functional characterization of nuclear genes coding for mitochondrial proteins and to knowledge of gene diseases related to mitochondrial dysfunctions. Indeed D. melanogaster is one of the most studied organisms and a model for the Human genome. Data are derived from the comparison of Human mitochondrial proteins versus the Drosophila genome, ESTs and cDNA sequence data available in the FlyBase database. Links from the MitoDrome entries to the related homologous entries available in MitoNuC will be soon imple-mented. The MitoDrome database is available at http://bighost.area.ba.cnr.it/BIG/MitoDrome. Data are organised in a flat-file format and can be retrieved using the SRS system.