A six-month-old shiba dog with a one-month history of progressive motor dysfunction showed clinical signs of a cerebellar disorder, including ataxia, dysmetria and intention tremor of the head. Histopathological and ultrastructural studies revealed distended neurons packed with membranous cytoplasmic bodies throughout the central nervous system. The activities of lysosomal acid β-galactosidase in its leucocytes and liver were less than 2 per cent of the control levels, and the compound accumulated in the brain was identified as GM1 ganglioside. A sibling which died immediately after birth was shown to have a β-galactosidase deficiency in the brain and visceral organs. A family study revealed that the sire and dam of the probands were heterozygotes with approximately half of the normal level of β-galactosidase activity, suggesting an autosomal recessive pattern of inheritance.