The magnitude of the rise in reticulocytes following the institution of therapy has been quite generally accepted as a means of evaluating the potency of various substances used in the treatment for pernicious anemia. The rate of the reticulocyte response and subsequent return to a normal level may also indicate the efficiency of the therapeutic substance used. The magnitude of the response of the reticulocytes will depend to some extent on the method of staining and the technic employed in counting the cells, on the initial erythrocyte count at the time treatment is instituted, on the presence of complicating disease conditions and perhaps on the age of the patient. If these factors are given due consideration, the form and magnitude of the reticulocyte curve serve as a rough index of the potency of various substances used, particularly if treatment is carried out perorally in the usual manner and the amount