TWO OF us (G. J. A. and H. L. S.), in 1952, published a report in the A. M. A.Archives of Internal Medicineof an unusual case of follicular lymphoma. 1 For a short time this patient had presented the clinical and laboratory findings of acute leukemia, and then these findings had spontaneously disappeared. Repeated lymph node biopsies proved that this patient had follicular lymphoma with sarcomatous changes. Subsequently we have been searching for the explanation of the peculiar cells ("notched nucleus cells" of Isaacs 2 ) which were typically present in the leukemic phase of that case. From a large number of leukemia cases we have studied a few in which "notched nucleus cells" were characteristically present. The results of these studies were briefly presented in the form of a lecture in May, 1953 3 ; a more detailed presentation of the subject is now being published elsewhere. 4 The