This FOA encourages applications for biomarker validation trials or exploratory clinical trials of drugs, biologics, surgical therapies or devices that may contribute to the justification for and provide the data required to design a future trial to confirm efficacy (i.e., a Phase III trial) in the treatment of neurologic disease. Applications for drugs or biologics should provide compelling scientific evidence that the investigational agent proposed for study will reach/act upon the designated target or that its mechanism of action is such that it will be of benefit in ameliorating a specific aspect of the disease. Diseases chosen for study should be based on the NINDS' strategic plan and clinical research interests (www.ninds.nih.gov/funding/areas/index.htm). Successful applicants will be given access to the NeuroNEXT infrastructure. The NeuroNEXT Clinical Coordinating Center (CCC) will work with the successful applicant to efficiently implement the proposed study. The NeuroNEXT Data Coordinating Center (DCC) will provide statistical and data management support. The NeuroNEXT clinical sites will provide recruitment/retention support as well as on-site implementation of the clinical protocol. Applicants do not need to be part of the existing NeuroNEXT infrastructure.