In this brief introduction an attempt is made to indicate some of the approaches to degenerative diseases of the nervous system and directions of future research. The details of the biochemical delineation of particular disease processes will be covered by others. Following will be an introduction to the biochemical approaches to genetically determined diseases which affect the developing nervous system. The sequence of characterization of most of these disease processes has followed the sequence of the prior authors. First, there has been the clinical delineation of a particular entity. Second is the careful clinical-pathologic correlation. A third step is often the introduction of genetic data as a part of the clinical description. The further steps relate to such areas as chemical pathology, determination of underlying biochemical mechanisms, and detection of heterozygotes. Finally, one would hope to be able to apply knowledge about the disease process to rational approaches to therapy and specific genetic counseling.