Nineteen cases of primary autoimmune haemolytic anaemia are reported in the dog. The clinical features included pale mucous membranes, weakness, lethargy and collapse. The intravascular haemolytic type of the disease was seen in nine cases and was characterised by evidence of haemolysis (eg, marked bilirubinaemia). The other 10 cases were classed as the extravascular destructive type of autoimmune haemolytic anaemia. The presence of autoantibodies (of the IgG class) and complement (C3) on the red blood cells from affected patients was demonstrated by a commercial Coombs' (antiglobulin) test which, although it has disadvantages, is satisfactory providing it is interpreted in association with the clinical, haematological and biochemical features. Treatment of these 19 dogs was with prednisolone and was successful in most cases.