CHA, a rare failure of erythrogenesis in infancy and childhood, has been re-examined on the basis of a review of 42 cases of our own and 133 others. Although the disease may have its onset late in gestation, severe anemia usually is not found at birth but, in 75% of cases, becomes apparent within the first 4 months. Associated congenital anomalies include abnormal thumbs, webbed neck and growth retardation. Treatment with corticosteroids as soon as the diagnosis is established induces a remission in 80% of patients. Thereafter, this therapy may need to be continued, often at an extremely low dosage level, sometimes intermittently, for many years before the hemoglobin value maintains itself without medication. Spontaneous remission has occurred in a few cases after years of transfusions. Although it has long been considered that the disease was a failure of normal erythrogenesis manifest by a normocytic normochromic anemia, more exact measurements reveal that the anemia is macrocytic, with MCV usually ranging between 100 and 115 mu3. Other abnormalities of the red cells are present; in general, these resemble characteristics of fetal erythrocytes rather than normal adult cells. These red cell changes may persist even after the patient has been in remission for years, thus representing a permanent abnormality in erythrogenesis.