A patient is described who, notwithstanding a strongly positive direct antiglobulin test with anti-IgG serum, apparently did not suffer from haemolytic anaemia. The survival of the patient's red cells, measured with 51Cr, was only slightly decreased. In vitro, the sensitized cells of the patient showed only a minimal tendency to adhere to monocytes. The patient's spleen functioned normally, since 51Cr-labelled donor erythrocytes, either sensitized with IgG-anti-D or damaged by heating, were eliminated rapidly from the circulation and sequestered in the spleen. These apparently contradictory findings could be explained by the fact that the patient's red cells were sensitized with autoantibodies, mainly belonging to the IgG4 subclass. Only weak IgG1 and IgG3 autoantibodies were detectable. Since previously the patient had suffered from a severe haemolytic anaemia, it is postulated that a switch has occurred from 'active' to 'inactive' IgG autoantibodies, perhaps induced by prednisone therapy.