Water stress in mature `Redhaven' / Lovell peach [Prunus persica (L.) Batsch] trees was imposed, during the 1988 growing season. Trickle irrigation was reduced from 100% to 25% of a calculated weekly evaporation amount on 22 June, 11 July, and 8 and 27 Aug. Trees were isolated from rainfall by tents under the canopy and from horizontal water movement between root systems on 4 sides to a depth of 0.5 m by a water-proof barrier. Canopy to air temperature differentials monitored throughout the growing season were developed into 3 stress indexes: crop water stress index (CWSI); cumulative crop water stress index (CCWSI); and postharvest cumulative crop water stress index (PCCWSI). CWSI values varied from 0 to 0.6, while both CCWSI and PCCWSI increased through late Sept. Mean PCCWSI of the 22 June 25% treatment increased at a greater rate than the other treatments. Significant linear regressions were found with some of the indexes and net photosynthesis or stomatal conductance; however, the r-square values were low. In general, no linear relationships were found between either CCWSI of PCCWSI and the Index of Injury for cold hardiness.