Our studies on the control of extracellular protease synthesis in an Aspergillus flavus strain isolated by us indicate that in a defined medium a protein must be present for enzyme to be produced. Soya bean protein and cotton seed protein were efficient inducers. The ability to induce enzyme synthesis was a characteristic property of the individual protein. Enzyme activity was not derepressed in the absence of a protein by limitation of nutrients. Cycloheximide blocked enzyme synthesis. Low levels (1%) of various carbohydrates did not repress enzyme synthesis, whereas most carbohydrates at 3% levels repressed enzyme synthesis. Addition of glucose to cultures actively producing the enzyme blocked further synthesis of enzyme. Addition of glucose to cultures producing the enzyme in the absence of sodium nitrate resulted in a decrease of enzyme activity.