In four cases of autoimmune hemolytic disease, rapidly developing anemia was associated with reticulocytopenia despite intensely erythroid bone marrow. Transfusions had been withheld because compatible blood could not be obtained, and each patient was virtually moribund on admission. Type-specific RBCs were administered promptly without reaction. From 2 to 84 carefully selected units were required to sustain life during the reticulocytopenic episodes, which lasted from a few days to more than six months. Transfusion in patients with autoimmune hemolytic anemia generally is unwise, because the autoantibody in the serum usually reacts with the RBCs of all potential donors, making a satisfactory cross match impossible. However, reticulocytopenia with profound anemia may present as a medical emergency in which prompt, careful transfusion is lifesaving.