To the Editor:—
Although our knowledge of the basic factors involved in the leukemic process and the relationship to nucleic acid metabolism is imperfect, there is ample evidence, both experimental and clinical, of the vital role of folic acid and vitamin B12 in normal hematopoiesis. Taking advantage of this fact, of course, has led to the clinical application of antimetabolites and, specifically, folic acid antagonists to therapy of the acute leukemias. Unnatural purines, such as 6-mercapto-purine, are also in use as blocking agents in the chain of nucleic acid synthesis for acute leukemia therapy. It seems irrational, therefore, to administer folic acid or liver to a patient with acute leukemia. The same contraindication to vitamin B12 seems probable, although there is conflicting evidence as to the specific role of this substance in nucleic acid metabolism of the leukocytic series. While this conclusion seems self-evident, there apparently is insufficient