Summary.The present report describes the occurrence of hemoglobinemia and hemoglobinuria in a patient with warm antibody hemolytic anemia in whom extensive studies failed to demonstrate the presence of a hemolysin or complementfixing antibody. Studies of the patient's red cells revealed only gamma globulin coating. Studies of the patient's serum revealed the presence of a γG globulin antibody capable of coating normal cells with gamma globulin but not with complement. No hemolysin could be demonstrated even with the use of special techniques known to enhance detection of hemolytic antibodies. Based on these negative findings and on previous experimental and clinical observations concerning the iso‐antibody, anti D, the possibility is raised that the hemoglobinuria observed in this patient resulted from extravascular red cell destruction of such magnitude that the capacity of the reticuloendothelial system to metabolize the products of red cell breakdown was exceed