Fluoro-Gold (F-G) has been used extensively as a fluorescent retrograde neuronal-track tracer in the past. We now report that intraperitoneal administration of 10 to 30 mg/ kg of F-G from 30 min to 7 days prior to sacrifice labels vascular endothelial cells of the brain, choroid plexus and meninges and can be used to assess vascular integrity and damage. F-G vascular labeling co-localized with rat endothelial cell antigen (RECA-1) in the membrane. F-G also intensely labeled the nuclei of the endothelial cells, and co-localized with propidium iodide staining of these nuclei. As well, the administration of F-G during neurotoxic insults produced by amphetamine, kainic acid or "penetrating" wound to the brain can detect where vascular leakage/ hemorrhage has occurred. Histological methods to detect F-G labeled brain vasculature were performed in the same manner as that used for fluorescent visualization of neuronal elements labeled with F-G after perfusion fixation and coronal sectioning (15 to 40 µm) of the brain. This in vivo F-G labeling of endothelial cells and their nuclei yields a clear picture of the integrity of the vasculature and can be used to detect changes in structure. Vascular leaks after "penetrating" wounds through the cortex and striatum, hyperthermic amphetamine exposure or excitotoxic kainate exposure were detected by F-G in the extracellular space and via parenchymal F-G subsequently labeling the terminals and neurons adjacent to the lesioned or damaged vasculature. Further studies are necessary to determine the extent of the leakage necessary to detect vasculature damage. Visualization of the F-G labeling of vasculature structure and leakage is compatible with standard fluorescent immuno-labeling methods used to detect the presence and distribution of a protein in histological sections. This method should be directly applicable to studying brain vascular damage that occurs in the progression of Alzheimer's disease, diabetes and for monitoring the brain vascular changes during development.