Effective and targeted delivery of cells to injured organs is critical to the development of cell therapies. However, currently available in vivo cell tracking methods still lack sufficient sensitivity and specificity. We examined, therefore, whether a highly sensitive and specific bioluminescence method is suitable to noninvasively image the organ distribution of administered mesenchymal stem cells (MSCs) in vivo. MSCs were transfected with a luciferase/neomycin phosphotransferase construct (luc/neo-MSC). Bioluminescence of these cells was measured (charge-coupled device camera) after treatment with luciferin, showing a linear increase of photon emission with rising cell numbers. To track these cells in vivo, groups of mice were injected with 1 x 10(5) luc/neo-MSCs/animal and imaged with bioluminescence imaging at various time points. Injection of cells in the suprarenal aorta showed diffuse distribution of cells in normal animals, whereas distinct localization to the kidneys was observed in mice with ischemia- and reperfusion-induced acute kidney injury (AKI). Intrajugular infusion of MSCs demonstrated predominant accumulation of cells in both lungs. In animals with AKI, detectable cell numbers declined over time, as assessed by bioluminescence imaging and confirmed by PCR, a process that was associated with low apoptosis levels of intrarenally located MSCs. In conclusion, the described bioluminescence technology provides a sensitive and safe tool for the repeated in vivo tracking of infused luc/neo-MSCs in all major organs. This method will be of substantial utility in the preclinical testing and design of cell therapeutic strategies in kidney and other diseases.