A synthetic medium containing 0.4% rutin, 0.3% (NH4)2HPO4, 0.1% KH2PO4, 0.1% MgCl2∙6H2O, and 0.8% (NH4)2SO4was developed for the production of the extracellular enzyme system that degrades rutin. The total amount of the enzyme system produced is approximately the same between 25 and 35 °C but the rate is more rapid at the higher temperature. Aeration is necessary both for synthesis and for excretion into the medium, excretion apparently being more sensitive than synthesis. Magnesium is required for growth and sulphate for release of the enzyme system into the medium. Calcium carbonate depresses both growth and production. The medium has been successfully employed for production in 5-gallon fermentors of the extracellular enzymes that degrade ruti