Parkinson’s disease: a chronic, progressive disease of the central nervous system, which involves the loss of nerve cells that reside in the brain, which produce a chemical called dopamine. Dopamine is a neurotransmitter that allows messages to be transmitted to the part of the brain that helps control and coordinate muscle movement. Parkinson’s symptoms appear when about 80% of dopamine-producing cells, have been lost. For this reason, people are not usually diagnosed until after age 55. The stem cell therapy is very promising because this disease is clearly related to the failure of a specific cell type when doing their work. It has been shown in both animal tests and clinical practice, that when dopamine is reintroduced into the central nervous system, symptoms diminish or reverse. Therefore, if stem cells can be induced to become dopamine neurons, either before or after transplantation into the brain, a complete recovery of cell function is theoretically possible.