Immunological data are reported from 19 cases of immune-mediated disease recorded in the old English sheepdog breed in Western Australia between 1978 and 1989. The conditions included autoimmune haemolytic anaemia (seven), idiopathic thrombocytopenia (one), Evans' syndrome (five), multiple myeloma (two), systemic lupus erythematosus (one), discoid lupus erythematosus (one) and hypothyroidism (two). The most consistent serological findings were raised serum IgG (60 per cent), depressed serum IgM (60 per cent) and the presence of multiple autoantibodies (anti-red blood cell 78 per cent, antinuclear antibody 44 per cent, rheumatoid factor 19 per cent). An underlying, breed-related disorder of immune regulation may account for these observations.