Citric acid production and biomass formation in submerged culture using Aspergillus niger from undersized semolina, with and without methanol, were analyzed using Gompertz, Logistic, Schnute, and Boltzman's models. They were compared statistically by using the F-test. Three-parameter models were statistically sufficient to describe the citric acid and biomass formation of A. niger. Citric acid and biomass formation rates (mu) ranged from 0.099 to 0.412 g/l/day and 0.173 to 0.744 day(-1), respectively. The lag phase duration increased from 0.387 to 3.281 and 0.087 to 0.824 days, respectively. Increased methanol concentration and the initial pH values of the medium had significant effects on the citric acid and biomass formation. (C) 2002 Elsevier Science Ltd. All rights reserved.