Six patients with chronic refractory autoimmune thrombocytopenic purpura (ATP) were treated with five doses of autologous red blood cells (RBCs) opsonized ex vivo with anti-RhO-(D) IgG. Increases in platelet counts were observed in all cases; complete responses requiring no further treatment--for periods of 8-72 months--were recorded in four patients, three of them splenectomized. The cost of the procedure was significantly lower than other "Fc receptor (FcR) blockade" treatments.