In 1924 one of us1definitely demonstrated for the first time the existence in normal human blood of pentose nucleotides. In 1931 we2reported the case of a man with acute myeloblastic leukemia who, following the intravenous injection of pentose nucleotides, made a remarkable temporary recovery. Since that time we have been much interested in therapeutic possibilities of these complex and highly reactive substances, which normally circulate in considerable amount in the blood and are known to exist principally in the nuclei of living cells. Occasional reports3have been made indicating that nucleic acid or its decomposition products have a stimulating effect on the white blood cell formation. In the latest of these reports, Reznikoff4described four cases of agranulocytic angina treated with transfusions of blood and intravenous injections of the purine bases, adenine and guanine. Three of his patients recovered. It should be pointed out