The purpose of this Funding Opportunity Announcement (FOA) is to encourage grant applications for investigator-initiated exploratory clinical trials to the National Institute of Neurological Disorders and Stroke (NINDS). The trials must address questions within the mission and research interests of the NINDS and may include Phase 1 and 2 studies of drugs and biologics, feasibility studies of devices, and early studies of surgical, behavioral or rehabilitation therapies. All exploratory trials must contribute to the justification for and provide some of the data required to inform a future trial to establish efficacy (such as a Phase 3, Phase 4 or Pivotal trial). This FOA uses the UG3/UH3 mechanism. Only projects that provide satisfactory progress in the UG3 phase may move to the UH3 phase, as outlined below. For a drug, biologic or device that has not completed a Phase 1/Early Feasibility trial: The UG3 mechanism will be used to plan and execute the Phase I trial(s). If Phase 1 trials are successful, the UG3 will also include the planning phase of a Phase 2 trial. The UH3 mechanism will then support the execution of the Phase 2 clinical trial. Transition to the UH3 will depend on successfully reaching agreed upon milestones. For a drug, biologic or device that has successfully completed the Phase 1/Early Feasibility trial(s), do not use this FOA. Instead use the Companion FOA XXX. For genetic studies, do not use this FOA. Instead, use FOA XXX.