3. Introduction

Intensive research over the past few years have elucidated, but not finally defined the etiology of Parkinson’s disease or the patophysiology of Huntington’s disease. Experimental animal models and cell culture studies have also helped to develop new treatment principles like neural transplantaion, renewed neurosurgical strategies and treatment with neurotrophic factors and glutamate antagonists. For Parkinson’s disease, actual clinical application of these treatments, combined with the now classic levodopa therapy, are rapidly evolving, and for Huntington’s disease corresponding experimental neural transplantations have been initiated.