This report discusses enhancement in cellulase production by Trichoderma reesei Rut-C30. A combination of 75 mM citrate buffer and low operating pH values; e.g., 3.5, resulted in about 100% higher enzyme production in shake flasks. A similar extent of improvement was seen at lower citrate buffer concentrations such as 5 and 10 mM. It is suggested that the undissociated form of citric acid is responsible for this improvement; no such acid moiety has been previously reported to enhance cellulase production.