This method allows precise analysis of the mechanism whereby chitosan/COS inhibit fungal growth. Interestingly, COS has also been proposed to function as a vaccine against a phytopathogen. This function involves sensing mechanisms and downstream activation of intracellular signaling networks that mediate plant defense responses. In the present study, the anti-dermatophytic activity of COS appears to involve a defensive response. Our future studies will address the detailed mechanism of this response.