Corncobs could serve as a substrate for citric acid production by Aspergillus niger. Methanol had a significant effect on fungal production of citric acid from corncobs. Of the four cultures examined, A. niger NRRL 2001 was found to produce the highest amount of citric acid (250 g/kg dry matter of corncobs) after 72 h of growth at 30 degrees C in the presence of 3% methanol. The yield of citric acid was over 50% based on the amount of sugar consumed.