More than half of the world’s population is infected with the Gram-negative pathogen Helicobacter pylori. Infection is associated with the development of peptic ulcers and an increased risk of gastric cancer. A major toxin secreted by H. pylori is the Vacuolating cytotoxin A (VacA). After secretion from the bacteria, the p33 and p55 subunits of the toxin bind to host cells, are internalized and cause severe “vacuolation”: the accumulation of large vesicles that possess hallmarks of both late endosomes and early lysosomes. The development of “vacuoles” has been attributed to pores formed by VacA channels. Apart from its vacuolating effects, VacA also directly affects mitochondrial function. Earlier studies suggested that the p33 subunit, but not the p55 subunit of VacA, could enter mitochondria to modulate organelle function. This raised the possibility that a mechanism separate from pore formation may be responsible for the effects of VacA on mitochondria, as crystallography studies and structural modeling predict that both subunits are required for a physiologically stable pore. Other studies have also shown that both the p55 and p33 subunits can indeed be efficiently imported into mammalian-derived mitochondria, raising the possibility that they could re-assemble to form a pore. Our research focuses on delineating the function and subcellular localization of the VacA subunits in order to assess their importance in pore formation. After raising anti-p33 and anti-p55 specific antibodies and performing cellular fractionations after incubation with host cells, our preliminary data shows that both subunits of VacA do indeed traffic to mitochondria.