Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker disease (GSS) and Fatal Familial Insomnia (FFI) are slow neurodegenerative disorders classified as transmissible spongiform encephalopathies (TSEs) or prion diseases, which appear in sporadic, hereditary or environmentally acquired forms. Tubulovesicular structures (TVS) are ultrastructural particles of unknown origin and chemical composition found in the brains of both animal and human forms of transmissible spongiform encephalopathies or prion diseases. In this paper, we report the results of a search for TVS in a total of 13 cases of sporadic Creutzfeldt-Jakob disease, three cases of Gerstmann-Sträussler-Scheinker disease, two cases of Fatal Familial Insomnia, and individual cases of familial, iatrogenic, and variant CJD (vCJD). TVS were found in all but one sporadic and one familial case of CJD. As controls, we examined 15 cases of Alzheimer's disease (AD), two cases of Pick's disease, and one case of multiple system atrophy. TVS were not present in any of these cases. This study confirms the TSE-specificity of TVS, the morphology of which suggests a possible pathogenetic role and relationship to recently described virion-like arrays of 25nm particles in scrapie-infected tissue cultures.