A disease of unknown aetiology has been observed in moose. The animals showed signs of a bovine viral diarrhoea/mucosal disease-like syndrome, and central nervous disturbances. Brains from adult female moose were investigated by means of histology, immunohistochemistry, electron microscopy, virology, and bacteriology. The results indicate that the nervous signs were not associated with a spongiform encephalopathy. The lesions suggest a viral aetiology, although all the virological investigations have so far proved negative.