According to the author''s concept, the various clinical manifestations of erythroblastosis fetalis in different infants can be traced to differences in the quality of the abnormal antibodies in the maternal serum. On this basis, two dis-tinct, though related, clinical syndromes can be distinguished: (1) Congenital hemolytic disease (with anemia and hydrops) due to the presence of univalent antibodies (glutinins or blockers) in the maternal serum, and (2) erythroblastosis proper (icterus gravis with or without anemia and kernicterus) due to bivalent antibodies (agglutinins), as a rule.