The discovery that embryonic stem cells, neural stem cells and potentially mesenchymal stem cells bear the potential to differentiate into neurons and glia in vitro and in vivo has opened a rapidly growing scientific field. Current research is very likely to impose a major impact on diagnosis and treatment of a variety of neuropsychiatric disorders. One of the paramount immediate goals of stem cell research is to develop tissue sources for restorative treatment of patients with Parkinson's disease. We have been able to develop predopaminergic cells derived from human embryonic or fetal midbrain that have been amplified in vitro for more than 2 years. These cells will hopefully enable restorative treatment of patients with Parkinson's disease in the near future.