The study of nucleic acids is one of the most rapidly developing fields in modern science. The exceptionally important role of the nucleic acids as a key to the understanding of the nature of life is reflected in the enormous number of published works on the subject, including many outstanding monographs and surveys. The pathways of syn thesis and metabolism of nucleic acid,s and the many and varied biological functions of these biopolymers are examined with the utmost detail in the literature. Nearly as much attention has been paid to the macromolecular chemistry of the nucleic acids: elucidation of the size and shape of their molecules, the study of the physicochemical properties of their solutions, and the appropriate methods to be used in such research. The surveys of the chemistry of nucleic acids which have been published so far deal almost entirely with their synthesis and, in particular, with the synthetic chemistry of monomers (nucleosides and nucleotides) ; less attention has been paid to the synthesis of poly nucleotides. There is yet another highly important aspect of the chemistry of nucleic acids which is still in the formative stage, the study of the reactivity of nucleic acid macromolecules and their components. This can make an important contribution to the deter mination of the structure of these remarkable biopolymers and to the correct understanding of their biological functions.