Transplantation of embryonic neurons can restore functional dopaminergic neurons in the brains of patients with Parkinson's disease. But while promising, cell transplantation therapy is still out of reach to the vast majority of patients, in part because of the inaccessibility of human embryonic tissue. On page 653, Arenas and colleagues describe a method for engineering virtually unlimited quantities of dopaminergic neurons needed for transplantation studies to treat Parkinson's disease. The authors first obtained neuronal stem cells from mouse cells transfected with a transcription factor that encourages cells to adopt a neuronal fate. They then co-cultured the cells with astrocytes, which release a factor that induces development into dopaminergic neurons. The engineered cells released dopamine, and some maintained the characteristics of dopaminergic neurons for up to two weeks after implantation into mouse brains.