Progress in stem cell biology research is enhancing our ability to generate specific neuron types for basic and applied studies and to design new treatments for neurodegenerative diseases. In the case of Parkinson's disease (PD), alternative human dopaminergic (DAergic) neurons other than primary fetal tissue do not yet exist. One possible source could be human neural stem cells (hNSCs), although the yield in DAergic neurons and their survival are very limited.In this study, we found that Bcl-XLenhances (one-to-two orders of magnitude) the capacity for spontaneous dopaminergic differentiation of hNSCs, which then exceeds that of cultured human ventral mesencephalic tissue. Bcl-XLalso enhanced total neuron generation by hNSCs, but to a lower extent. Neuronal phenotypes other than DA were not affected by Bcl-XL, indicating an exquisitely specific effect on DAergic neurons.In vivo, grafts of Bcl-XL-overexpressing hNSCs do generate surviving human TH+neurons in the adult rat 6-OH-dopamine lesioned striatum, something never seen when naive hNSCs were transplanted. Most of the data obtained here in terms of the effects of Bcl-XLare consistent with an enhanced survival type of mechanism and not supportive of induction, specification, or proliferation of DAergic precursors.From thisin vitroandin vivoevidence, we conclude that enhancing Bcl-XLexpression is important to obtain human DAergic neurons from hNSCs. These findings may facilitate the development of drug-screening and cell-replacement activities to discover new therapeutic strategies for PD.