It was possible to trace real-time change of redox balance in a plant in vivo by a spin probe-ESR method, after exposing it to various physical and chemical stresses. Consequently, a strong light, a cold spray, and NO2 and O-3 gases were found to lead to relatively oxidative states in broccoli sprouts, but SO2 and CO2 did not influence the redox balance in the sprouts in the dark.