This project encompasses collaborative studies undertaken by the Office of the Chief. A major initiative involves the study of the etiology of Parkinson's disease (PD) using the twin pair registry of the National Academy of Sciences/National Research Council. The prevalent cases of PD in the more than 6,000 twin pairs in which both members are alive, will be identified. This study will evaluate: environmental, medical and family histories of both affected and unaffected members of the twin pairs; and measurement of progression of disease over time. This project will investigate genetic and environmental contributions and their interactions to the etiology of PD. A Cooperative Agreement was funded for the clinical aspects of this study. BFSB provided statistical coordination and data management. This project has been directed by Dr. Jonas H. Ellenberg. With Dr. Ellenberg's departure from NINDS, the Branch has continued to provide limited data management support for the project. International analytic surveys of neurological diseases reported under this project in FY 1994 are now reported in Project ZO1 NS 02652-11 BFSB, Statistical Collaboration and Consultation.