AbstractRecent studies have shown that GTP‐binding proteins can modulate mitochondrial membrane fusion and fission. Furthermore, GTP‐binding proteins can regulate the binding of ribosomes to the mitochondrial membrane and may facilitate the import of proteins through contact points between inner and outer mitochondrial membranes. Mitochondrial GTP‐binding proteins therefore appear to have the potential to modulate physiological function of the organelle and may also be involved in cellular processes such as cellular transformation. A beginning has been made on the characterization of mitochondrial GTP‐binding proteins and the DNA sequence of one protein has become newly available. Future studies are needed to determine whether GTP‐binding proteins are interacting with cell signalling molecules such as protein kinases in the mitochondria. Copyright © 2002 John Wiley & Sons, Ltd.