Tomato plants were studied to assess the potential value of ethanol accumulation in plant tissue as a measure of O2 stress resulting from short periods of soil flooding. Ethanol concentration in xylem exudate was markedly associated with air temperature, and to a lesser extent with light intensity and soil temperature under conditions of flooding. Field flooding results agreed closely with simulated environments.A small amount of ethanol was eliminated by transpiration from flooded tomato plants under environmental conditions that favored accumulation. A slightly higher amount of ethanol was excreted from the roots.Ethanol in tomato plant samples appeared to indicate the intensity of O2 deficiency during flooding by reflecting both soil O2 supply and environmental effects, and could serve as a useful indicator in relating tomato plant injury to flooded conditions.