The dismal prognosis for patients with Glioblastoma Multiforme asks for new treatment modalities that circumvent the problems of the Blood Brain Barrier, the heterogeneity of the tumour cells, and their extensive infiltrative nature. Such treatment options may consist of more specific targeting of drugs and better delivery techniques. It has been shown that Neural Stem Cells (NSCs) can migrate towards a intracerebral tumour in vivo and have the capacity to track infiltrating tumour cells. Their migratory capacities make NSCs promising delivery vehicles in the therapy of brain tumours. The use of NSCs as killing messengers , which can deliver tumour attacking compounds, has been investigated intensively in the last few years. New findings indicate that NSCs might not only serve as magic bullets that can be loaded with tumour killing agents, they seem to have the intrinsic capacity to restrain tumour growth. NSCs might thus be endogenous inhibitors of tumour development. However, it is yet not clear how NSCs inhibit the growth of tumour cells. Two general possibilities might be important here. First NSCs need to be in direct contact with the tumour, thus cell-cell contact is needed, or second NSC`s might release substances with tumour-growth inhibiting capacities. We observed that NSC conditioned media clearly diminished the growth of glioblastoma tumour cells. These results suggest the presence of substance that affects tumour cells in conditioned media, which indicates that NSCs produce and release a substance which affects the growth of tumour cells. Our aim is to further elucidate the growth inhibitory capacities of NSCs. Additionally, the nature of the substance responsible for the growth inhibitory effect will be investigated. Used techniques are Flow Cytometry, Immunocytochemistry, Cell vialbility assays, Proteomics and Functional Genomics approaches.