Anatomical and behavioral characterizations of neural transplants, whether within (allograft) or across (xenograft) species, have provided evidence that the transplant survives, integrates with the host tissue, and may lead to functional recovery. Several animal models of neurodegenerative disorders demonstrate the feasibility of using neural transplantation as an alternative treatment for these human diseases. While more elaborate basic animal studies are needed, clinical trials have begun. Neural transplantation is currently used as an experimental treatment for Parkinson's disease and several investigators have suggested using the same treatment procedure for other neurodegenerative disorders, such as Huntington's and Alzheimer's disease.