1. A method for the combined demonstration of erythrophagocytosis, agglutination, and hemolysis was developed and applied to the study of a series of antierythrocytic antibodies under varying conditions of temperature and pH, using normal, trypsinized, and PNH corpuscles. Erythrophagocytosis was observed supravitally and in fixed preparations.
2. Only those antibodies which were potentially or actually hemolytic produced phagocytosis under the experimental conditions employed. The conditions necessary for the production of the two phenomena were similar except in the case of anti-A. In titration experiments, erythrophagocytosis occurred in higher serum dilutions than did hemolysis.
3. All the antibodies producing opsonization required the presence of thermolabile components of fresh serum for optimal activity. Except with anti-A, appreciable erythrophagocytosis was not produced by heat-inactivated sera. Hemolysis produced by systems other than antibody and complement was unaccompanied by phagocytosis.
4. It is suggested that hemolysis and erythrophagocytosis may both result from the same type of alteration of the red cell surface.