The quantity of some of the molecular components of Streptomyces orientalis was markedly altered during the biosynthesis of vancomycin. The addition of elevated levels of inorganic phosphate caused changes in the amount of total carbohydrates, nitrogen, phosphate, DNA, RNA, and alkaline phosphatase in the cell during the fermentation. An excess amount of this ion also caused a decrease in the quantity of vancomycin synthesized as well as a lag in the time when synthesis was initiated. The possibility of a correlation between the biosynthesis of alkaline phosphatase and vancomycin is discussed.