BACKGROUND: Stem cell therapy is especially interesting for inner ear related diseases, since the hair cells are very sensitive and do not regenerate. Hair cell loss is therefore irreversible and is accompanied by hearing loss. In the last few years, different research groups have transplanted stem cells into the inner ear with promising results. In the presented study, our aim was to gain insight into how neuronal stem cells behave when they are transplanted, both in vitro and in vivo, into a damaged inner ear. METHODS: Neuronal stem cells from E9.5 day old mouse embryos were collected and infected with an adenoviral vector encoding green fluorescent protein (GFP). GFP+ cells were then transplanted into a damaged organ of Corti in vitro or into a damaged mouse inner ear in vivo. RESULTS: We were able to detect GFP+ cells close to the organ of Corti in vitro and in the organ of Corti in vivo. The GFP+ cells do not seem to be randomly distributed in either the in vitro or in vivo situation. Most interestingly, GFP+ cells could be detected close to places where hair cells had been lost in vivo. CONCLUSION: Neuronal stem cells are interesting candidates to replace lost hair cells. However, a great deal of research is still needed before they can enter clinical trials.