1. Three patients with untreated pernicious anemia were transfused with packed erythrocytes to produce a normal hematocrit before they were treated with vitamin B12. One patient with untreated pernicious anemia was transfused with 250 cc. plasma prior to therapy with vitamin B12. No significant changes were noted in this patient who received plasma.
2. Following erythrocyte transfusions the bone marrows of these patients were considered to show the megaloblastic type of maturation with a reduction in percentage of the early megaloblasts (Stages I and II). The ME ratio of the marrows increased. A decrease in the absolute reticulocyte count occurred. No change occurred in the peripheral leukocyte and platelet counts and there was no significant change in the clinical condition of the patients.
3. After therapy with vitamin B12, at a time when the hematocrits were normal, the bone marrows became normoblastic, a small but definite reticulocytosis occurred, the leukocyte and platelet counts returned to normal, and there was subjective improvement in the condition of the patient.
4. It is concluded that in these three patients with untreated pernicious anemia multiple transfusions of packed erythrocytes decreased erythropoiesis but did not cause any basic change in the type of erythrocyte maturation.