Introduction. —During recent years, and especially since the introduction of the sodium citrate method, blood transfusion has become one of the most common forms of treatment of the various types of primary and secondary anemias. Thus far, however, little is known as to the length of life of the transfused erythrocytes in patients with primary and secondary anemia, and until the recent work of Ashby1 no observations had been made on this subject. This investigator studied the length of life of transfused red corpuscles in pernicious anemia and found the average to be about three months. Previous to this time various observers had claimed the length of life of the red corpuscles to be from fourteen to fifty-two days.2 Information on this point seemed desirable in that it might demonstrate the practical value of transfusion, serve as an aid in deciding what the proper intervals between transfusions should be, and