Although gray matter lesions involving neurones and astrocytes are prominent in human transmissible spongiform encephalopathies (TSE), white matter lesions have also been occasionally observed. Secondary (Wallerian) degeneration and direct myelin damage have been invoked, but the physiopathology of white matter involvement is still debated. We performed an immunohistochemistry study with anti-PrP antibodies of autopsy material of four patients with Creutzfeldt-Jakob disease (CJD), together with transmission electron microscopy (TEM) studies of conventionally processed biopsy specimens of the same patients. Light microscopy immunolabeling was observed as arrays adjacent to myelinic fibers and as a clumps adjacent to oligodendroglial nuclei; both cerebrum and cerebellum were involved. At the ultrastructural level, two types of intracellular inclusions were seen in the white matter. They were associated with dense lysosomes in oligodendroglial perikarya and in their processes. The inclusions were made of finely fibrillar, paracrystalline, amorphous, or densely osmophilic material. Thus, our findings may suggest that white matter involvement in spongiform encephalopathy is due to direct modifications of oligodendroglial cell associated with abnormal metabolism of PrP.