A method has been developed which allows identification and quantitation of red cell-bound immunoglobulins and complement in canine blood. The technique utilizes ELISA methodology and the assay identifies cases of autoimmune haemolytic anaemia which are negative by the Direct Coombs test. Further, the amount of antibody present on the red cells shows a close correlation to the haemoglobin level; suggesting that the degree of sensitization of the RBCs influences their rate of destruction. Favourable response to treatment correlates with a decrease in the levels of bound antibody and complement.