Sensor histidine kinases (HKs) are important factors that control cellular growth in response to environmental conditions. The expression of 15 HKs from Aspergillus nidulans was analyzed by quantitative real-time PCR under vegetative, asexual, and sexual growth conditions. Most HKs were highly expressed during asexual growth. All HK gene-disrupted strains produced reactive oxygen species (ROS). Three HKs are involved in the control of ROS: HysA was the most abundant under the restricted oxygen condition, NikA is involved in fungicide sensing, and FphA inhibits sexual development in response to red light. Phosphotransfer signal transduction via HysA is essential for ROS production control.