Spinal cord samples from IM or VM mice injected intracerebrally with the 87V scrapie agent were examined ultrastructurally at the clinical stage of disease for changes in blood vessel permeability and for pathological alterations. In several animals, (3 of 16), massive changes were noted in the cervical spinal cords in the subependymal area of the cortical gray matter immediately surrounding the central canal including ependymal cell changes, the presence of amyloid plaque in close association with microglial cells, extensive neuropil vacuolation, the appearance of reactive astrocytes, degenerating neurites and vacuolated neurons. In those regions showing structural damage, localized increased permeability to horseradish peroxidase across the blood-brain barrier was noticed along with the appearance of numerous vesiculo-canalicular profiles in micro-blood vessel endothelial cells with extravasation of the tracer to the neuropil. Some damaged neurons appeared flooded with this tracer. These changes were not observed in either the thoracic or lumbar spinal cord regions. The occurrence of pathological changes in the spinal cords of a small percentage of intracerebrally injected mice was probably due to a high concentration of the scrapie agent which localized in the cervical spinal cord, presumably after entering the spinal fluid via the lateral ventricle at the time of injection.