PROJECT SUMMARY/ABSTRACT This proposal outlines plans to collect and share biospecimens with the Biospecimen Exchange for Neurological Disorders (BioSEND) repository, the National Institute of Neurological Disorders and Stroke (NINDS) biomarker repository. This administrative supplement would build on the aims of a recently awarded R01 which will evaluate potential microbiome-gut-brain mechanisms in prodromal and symptomatic Lewy body diseases. The R01 will be recruiting a unique study cohort, which includes participants with idiopathic rapid eye movement (REM) Sleep behavior disorder (iRBD). REM Sleep Behavior Disorder is one of the earliest and most specific indicators of Lewy body diseases, providing a prodromal cohort to evaluate early disease mechanisms. Additionally, we will be enrolling two symptomatic cohorts, a Parkinson’s disease cohort (PD) and Dementia with Lewy body disease (DLB) cohort. These cohorts provide an opportunity to conduct a novel evaluation of the presence of a bloom in sulfate reducing bacteria/dysbiosis and intestinal permeability. We will determine if these are present early in the disease and are associated with known disease processes (increases in α-synuclein, midbrain degeneration and clinical outcomes). The R01 project will evaluate these key mechanisms through the collection of urine, blood, and stool biospecimen samples in addition to advanced MRI and a breath test. This administrative supplement would support sharing of these biospecimens with BioSEND, which banks biospecimens for more than 50 different studies. The repository is developed to support high quality data collection and banking, providing specimens available to researchers around the world. The administrative supplement will support the implementation of study specific manual of procedures already developed by BioSEND to facilitate sharing of biospecimens. BioSEND’s goal is to make it easy for researchers to identify the samples they need for their research through online biospecimen catalogs that can be queried by approved researchers. The administrative supplement would support sharing of this unique cohort with investigators around the world. This will increase the R01 project’s likelihood to exert a sustained, powerful influence on the study of Lewy body diseases.