We recently compiled a complete list of phosphorelay signal transduction components in the model filamentous fungus Aspergillus nidulans. In this study, we characterized a histidine protein kinase (designated NikA) that is found in many fungi, with special reference to responses to potent fungicides (iprodione and fludioxonil). We provided evidence that not only NikA, but also two downstream response regulators (SskA and SrrA) are crucially implicated in the mode of action of these fungicides, and also that the further downstream HogA-MAPK cascade is exaggerated abnormally (or ectopically) in hyphae by the fungicides in a manner dependent on the NikA-SskA phosphorelay.