Since 1985 a novel clinical syndrome with insidious onset and a progressive course leading to slaughter after 1-6 months has been observed in 10 Friesian/Holstein cattle aged between 3 and 6 years in 4 dairy herds in different areas of England. Rarely, sudden death is seen. Early clinical signs have included apprehension, hyperaesthesia and incoordination, which progressed to fear and aggression with increased incoordination and even falling. Eventually unpredictable behaviour, frenzy or recumbency necessitated slaughter. Histopathological examination demonstrated bilaterally symmetrical degenerative changes in certain brain stem grey matter locations with neuropil and neuronal vacuolation. Fibrils resembling scrapie associated fibrils were seen in a homogenate of brain tissue from one affected cow. Until further characterisation has been achieved it is suggested that this disorder is called bovine spongiform encephalopathy.