Cell transplantation to the brain and spinal cord is a well-established research tool for studies on cellular and molecular mechanisms, but can it be developed into a useful therapuetic approach in human neurological disorders? Clinical trials in patients with Parkinson's disease have provided encouraging evidence, however, no treatment based on transplantation is available yet. An overview of current research is given in this book. It summarizes the status of grafting in humans and discusses scientific problems that have to be solved before intracerebral transplantation can become a useful routine approach to treatment.