The experiment described herein was performed in order to establish a completely synthetic medium for growing P. denitrificans cells. In order to obtain in 48 hr. a growth as good as that obtained with the control cultures (with yeast extract), the medium must be formed by micronutrients, the inorganic salts No2SO4, MgSO4 and (NH4)2SO4,and by an amino acid such as sodium glutamate. The KNO3 is for course needed in order to proporcionate the nitrate, and the medium must be buffered with 1M potassium phosphate buffer, pH 6.8. Succinate serves as a substrate. The role of glutamate is under investigation.