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Water deficits must be imposed on crops during non-critical growth periods to maximize net economic output per unit of water consumed by the plant. The reference ET-crop coefficient procedure widely used for managing fully irrigated crops would be easiest to implement for irrigation management of deficit irrigated crops provided the water stress coefficient (Ks) used in the procedure was more responsive to plant water stress. The objective of this paper was to further investigate the use of a canopy temperature (Tc) ratio calculated as a quotient of Tc measured over a fully irrigated crop divided by Tc measured over the water stressed crop as a substitute for Ks presently used in the reference ET-crop coefficient irrigation scheduling procedure. Four irrigation levels were imposed on corn (Zea mays L.) ranging from fully irrigated to 55% of seasonal ET applied at critical growth stages. Canopy temperature was continuously monitored in the four treatment levels and the Tc ratio was computed for the warmest period of the day (1300 to 1500 h MST). Crop ET was calculated solely as reference ET multiplied by the basal crop coefficient times the Tc ratio to estimate soil water deficit (SWD) with a water balance. This SWD estimate was compared to the SWD estimated by the traditional reference ET-crop coefficient-Ks procedure and measured SWD. The estimated SWD via the Tc ratio technique compared favorably with measured SWD for the 55% ET treatment. Advantages of this technique is that it does not require knowledge of soil water properties such as field capacity and total available water as well as the crop root depth.