Synopsis: Evapotranspiration rates of 75‐ and 100‐cm. crops of sudangrass were similar and considerably larger than that of the 140‐cm. height. This difference appeared to be due to the presence of seedheads rather than physiological maturity. It was also shown, for days of similar energy input, that evapotranspiration increased with wind speed. These facts emphasize the point that for well‐watered sudangrass, physical rather than physiological factors regulated the evapotranspiration.