Mitochondria, important energy centers in the cell, also control sperm cell morphogenesis. Drosophila spermatids have a remarkably large mitochondrial formation called the nebenkern. Immediately following meiosis during sperm development, the mitochondria in the spermatid fuse together into two large aggregates which then wrap around one another to produce the spherical nebenkern: a giant mitochondrion about 6 micrometers in diameter. The fused mitochondria play an important role in sperm tail elongation by providing a structural platform to support the elongation of sperm cells. We have identified a novel testis-specific protein, Spermitin (Sprn), a protein with a Pleckstrin homology-like (PH) domain related to Ran-binding protein 1 at its C-terminus. Fluorescence microscopy showed that Sprn localizes at mitochondria in transfected Kc167 cells, and in the nebenkern throughout spermatid morphogenesis. The role of Sprn is unclear, as sprn mutant males are fertile, and have sperm tail length comparable to the wild-type.