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Corn is highly dependent upon soil moisture availability to generate consistent and favorable yield. The objective of this study was to assess photosynthesis responses of corn hybrids to drought stress intensities with and without known drought tolerance mechanisms. The six commercial hybrids, three drought tolerant, DKC 65-81, P1498, and N75HGTA, and three standards hybrids with similar maturities, P1319, DKC 66-97, and N77P3111, were grown in four sunlit, controlled environmental chambers for 38 days. Four variable soil moisture treatments were achieved by manipulating irrigation based on evapotranspiration of control treatments starting at two weeks after planting. Plant biomass was measured at the final harvest, 38 days after planting. Leaf gas exchange parameters were measured five times during the stress treatment period. Photosynthesis, stomatal conductance, and transpiration rates declined in all corn hybrids with declining soil moisture levels. Even though significantly higher values of these gas exchange parameters were observed under optimum and across a wide range of soil moisture conditions for the drought tolerant hybrids compared to non-drought hybrids, the rate of declines of these parameters with unit decrease in soil moisture content were not different between the two groups of hybrids. These results suggest that greater rates of gas exchange properties and associated biomass production was achieved by increasing the potential photosynthesis under optimum conditions. The stress response, however, is not modified among the two groups of corn hybrids. This suggests that breeding should focus not only increasing potential photosynthesis, but also its response to drought conditions to be able to produce higher biomass and greater yield. Key words: Drought tolerance, maize, photosynthesis, droughtgard, aquamax, artesian Abbreviations: DAP, Days after planting; SPAR--Soil-Plant-Atmosphere-Research; TD, Total dry weight; Pn, Photosynthesis; [g.sub.s], stomatal conductance; Tr, Transpiration rate; Fv'/Fm', fluorescence; WUE, Water-use efficiency, INTRODUCTION Corn (Zea mays L.) is among the top three of the most widely grown crops in global agriculture with a total production of 960 million metric tons in 2015 [...]