Description of seven cases of kwashiorkor in children of one and a half to eight years of age, in which at one time or other an aplastic crisis (erythroblastopenia) occurred with the appearance of giant proerythroblasts or their precursors in the bone marrow. This condition independent of the treatment—reversed to normal in four cases and was followed by a reticulocytic crisis. Three of the children died during or shortly after the aplastic crisis. The author considers erythroblastopenia in these cases as due to insufficiency of the bone-marrow (lability) caused by chronic protein deficiency superimposed by frequent infections. The giant pro-erythroblasts are pathologic forms of erythropoiesis and are not identical with Ehrlich’s megaloblasts.