The present invention are directed to P.sup.1, P.sup.4-di(uridine 5'-)tetraphosphate, tetra-alkali metal salts such as tetrasodium, tetralithium, tetrapotassium, and mixed tetra-alkali metal cations thereof. The tetra alkali metal salts of P.sup.1, P.sup.4-di(uridine 5'-)tetraphosphate are water-soluble, nontoxic, and easy to handle during manufacture. These tetra-monovalent alkali metal salts are more resistant to hydrolysis than the mono-, di-, or tri-acid salts, therefore, they provide an improved stability and a longer shelf life for storage. The present invention also provides methods for the synthesis of P.sup.1, P.sup.4-di(uridine 5'-)tetraphosphate, and its pharmaceutically acceptably acceptable salts thereof, and demonstrates the applicability to the production of large quantities. The methods substantially reduce the time required to synthesize diuridine tetraphosphate, for example, to three days or less.