The filamentous fungi Aspergillus oryzae and A. niger grow by apical extension of multinucleate hyphae that are subdivided into compartments by cross-walls called septa. Submerged cultivation, image analysis, and fluorescence microscopy were used to study the role of the carbon source on mitosis and hyphal extension in these fungi. In the two species of Aspergillus, the length of the apical compartment, the number of nuclei in the apical compartment, and the hyphal diameter were regulated in response to the surrounding glucose concentration. A long apical compartment with many nuclei was the result of a high glucose concentration, whereas a short apical compartment with few nuclei was the result of a low glucose concentration. This is the first study of the influence of glucose concentration on nuclear mitosis and septation in filamentous fungi grown submerged. In addition, this is the first time a model of the duplication cycle in higher filamentous fungi has been simulated. (C) 2000 John Wiley & Sons, Inc.