The conversion of synthetic root exudates, i.e. of a mixture of amino acids, organic acids and sugars, added to soil in a single dose or continuously, was studied. After the addition of a single dose, the root exudates were gradually mineralized and after 76 hours, 85% of carbon had been released in the form of carbon dioxide. The extent and rate of mineralization was not influenced by the simultaneous addition of ammonium phosphate. The continuous addition of substrate formed a model artificial rhizosphere. In the steady state, 93% of the carbon in the added substrate was mineralized to carbon dioxide. The conversion of organic acids, sugars and amino acids and the mineralization of nitrogen was studied simultaneously by chromatography. In soil continuously enriched with root exudates, phenomena similar to the rhizosphere effect in nature were observed both in the numbers of microorganisms and in the relative incidence of the nutritional groups of bacteria.