Water use efficiency for plant production (WUE) can vary among different species and different climates and weather variables. However, by introducing the saturation deficit as a normalizing factor, the relationship is relatively constant even under different environmental conditions. The aim of this study was to determine the equivalent transpiration (ET) and the equivalent evapotranspiration (ETE) for corn and soybean in different phenological substages. Five growth seasons in corn and one in soybean were used to determine the relation in the province of Buenos Aires, Argentina. Another cycle of soybean in the state of Minas Gerais, Brazil, was used for soybean. Subperiods were: emergence-flowering (E-F); flowering-physiological maturity (F-PM) and emergence-physiological maturity (E-PM) ET in corn for E-PM was 7.5 g/k.kPa and its C.V. between growing seasons reduced from 8.7 % to 0.3 %. Corn ETE at E-PM was 4.2 g/k.kPa and for E-F and F-PM substages, were 4.2 and 4.3 g/k.kPa respectively. C.V. decreased from 29 % to 19 % in E-F and from 32 % to 17 % in F-PM. In soybean, ETE was 0.92 g/k.kPa in the E-F interval. Data from F-PM stage are being processed and will be included in the final paper.