Electron microscopic examination of brain biopsy specimens from two patients with Creutzfeldt-Jakob disease revealed the presence of intracellular membranous spiral inclusions in the processes of cortical cells. These inclusions, 375 nm to 660 nm in length and 50 nm to 88 nm in width, resemble similar structures reported in a patient with the same disease by Bastian and, more recently, in a second patient by Gray et al. These inclusions bear close morphologic resemblance to spiroplasma organisms, a wall-free prokaryote known to cause a "slow-virus"-like disorder in mice.