The pathologic changes visible in infants with erythroblastosis are caused by erythrocyte destruction. They vary with the severity of the disease and consist of the deposit of iron especially in the liver, kidneys, and spleen, in excessive stimulation of erythrocyte formation in the liver, and in initiation of erythropoiesis in areas in which erythrocytes are not normally formed, especially the kidneys. Erythroblasts are commonly present in excessive number in the capillaries of the lungs; this may be the only evidence of erythroblastosis in macerated fetuses. Severe prolonged postnatal hyperbilirubinemia leads to deposit of bilirubin with resultant yellow discoloration of parts of the brain. The most severely affected infants are generally hydropic and die within 1-2 hours of birth. Mildly affected infants or those who survive for several days following birth may show no pathologic evidence of erythroblastosis.