Do "gene therapies" offer new approaches to the treatment of Parkinson's disease? The presentations of this symposium, as well as numerous published articles, suggest that they might. This article describes a preclinical in vivo gene therapy study in parkinsonian monkeys and briefly reviews the history of studies with novel cellular implantation approaches to Parkinson's disease as a basis for evaluating when and how gene therapy trials in Parkinson's patients might be appropriate. A number of concerns are raised.