Microbiological production of Xanthosine 5'-monophosphate sodium salt (XMP) in high yields opens the way for its use in foods as a flavoring agent and as a chemical intermediate for production of purine antimetabolites. Xanthosine 5'-monophosphate sodium salt also should prove valuable in the production of synthetic polynucleotides for studies on the genetic code, protein synthesis, and nucleic acid structure.