The present invention provides new methods for the synthesis of the therapeutic dinucleotide, P.sup.1,P.sup.4-di(uridine 5')-tetraphosphate, and demonstrates applicability to the production of large quantities. The methods of the present invention substantially reduce the time period required to synthesize diuridine tetraphosphate, preferably to three days or less. The novel tetrammonium and tetrasodium salts of P.sup.1,P.sup.4-di(uridine 5')-tetraphosphate (Formula I) prepared by these methods are stable, soluble, nontoxic, and easy to handle during manufacture. ##STR00001## wherein: X is Na, NH.sub.4 or H, provided that all X groups are not H.