The utilization of L(+)-tartrate in Aspergillus flavus is constitutive. The use of tartrate by these cells is inhibited by the metabolic poisons 2,4-dinitrophenol and sodium azide. Glucose, mannose, and sucrose at high extracellular concentrations prevent the utilization of L(+)-tartrate by the young mycelium. Ammonium ion increases the inhibition due to glucose, while the addition of ferric ions to the external medium prevents the glucose-induced inhibition of tartrate utilization.