Neuronal alterations in the cortex of hamsters with experimental Creutzfeldt-Jakob disease (CJD) were studied utilizing the rapid Golgi and Golgi-Hortega methods. In terminally ill hamsters many pyramidal neurons showed a considerable decrease in the number of dendritic spines often with moderate irregularities in size. The shafts of apical dendrites in some cortical pyramidal neurons were tortuous. Occasional neuronal cell bodies were irregular in contour and showed hole-like empty spaces. Two types of focal swellings, which involved both axons and dendrites, were observed; focal swellings were either semitranslucent or darkly impregnated. Possible mechanisms for the pathogenesis of the semitranslucent and dark swellings are discussed. The neuronal changes showed no preponderance for a particular neuronal group or for selective segments of individual neurons.