Summary: In four patients with autoimmune hemolytic anemia, antiglobulin testing revealed, in addition to IgG, C3 and C4, erythrocyte-bound C5 and C6. In the presence of fresh serum, Rh-antiserum Ripley also caused non-lytic binding of C3, C4, C5 and C6 to normal type O, CDe red cells. These studies indicate that late-acting complement components (C5, C6) may be present on red cells of patients with immune hemolytic anemias without overt disruption of membrane integrity.