Perturbation of cell wall synthesis in Saccharomyces cerevisiae, either by mutations in cell wall synthesis-related genes or by adding compounds that interfere with normal cell wall assembly, triggers a compensatory response to ensure cell wall integrity. This response includes an increase in chitin levels in the cell wall. Here it is shown that Aspergillus niger also responds to cell wall stress by increasing chitin levels. The increased chitin level in the cell wall was accompanied by increased transcription of gfaA, encoding the glutamine : fructose-6-phosphate amidotransferase enzyme, which is responsible for the first and a rate-limiting step in chitin synthesis. Cloning and disruption of the gfaA gene in A. niger showed that it was an essential gene, but that addition of glucosamine to the growth medium could rescue the deletion strain. When the plant-pathogenic fungus Fusarium oxysporum and food spoilage fungus Penicillium chrysogenum were subjected to cell wall stress, the transcript level of their gfa gene increased as well. These observations suggest that cell wall stress in fungi may generally lead to activation of the chitin biosynthetic pathway.