Aleutian disease was diagnosed as the cause of posterior ataxia and paresis in domestic ferrets. Six serologically positive animals (four clinically affected and two unaffected) were investigated in detail and seven other clinically affected ferrets were also identified. The diagnostic findings included hypergammaglobulinaemia, histological lesions in the central nervous system and parvovirus-like particles in mesenteric lymph nodes. A wider serological survey of 446 animals owned by members of a ferret club revealed an incidence of 8.5 per cent seropositive animals.