A case of severe but transient haemolytic disease occurring after a febrile episode is described. The thermal amplitude of the haemolysin was high during the acute phase, since the autoantibody fixed complement at 31 degrees C. After 4 months complement fixation could exclusively be demonstrated at 4 degrees C. The patient was treated in a room heated to 30-32 degrees C. The treatment consisted of prednisone and azathioprine and during the acute phase plasmapheresis was attempted in order to reduce the antibody concentration. However, the haemolysis decreased when the thermal amplitude of the antibody diminished. 1 year after termination of therapy, she developed sarcoidosis.