Severe glial reaction (gliocytosis) in hamsters infected with the 263K strain of scrapie is described. Gliocytosis is an extremely rare phenomenon in scrapie-affected mice. In hamsters, however, it forms an important and stable feature of the neuropathology. Both astrocytic hyperplasia and hypertrophy are described. The author discusses briefly the possible contribution of the scrapie agent and of the host use in the experiments described here to the development of glial changes.