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In order to assess how plant water potential is related to soil water availability and evaporative demand, determinations of diurnal and seasonal plant water potentials between 23 April 1997, and 22 September 1998, were studied in Acacia berlandieri Benth., a native shrub of the northeastern region of Mexico. Average plant water potentials during the wettest period ranged from -0.37 MPa (predawn, PD) to -2.79 MPa (midday, MD) whereas, during the long, hot, and severe drought period PD and MD water potentials measurements diminished down to -5.9 and -6.8 MPa, respectively. Average diurnal depression of plant water potential (calculated as the difference between midday and predawn water potentials) during the wettest and driest season varied from -2.28 +/-0.50 MPa to -0.86 +/- 0.46 MPa, respectively. An exponential function was found between PD water potential with average soil water content and vapor pressure deficit (VPD). Both variables supported about 85% and 66%, respectively, of the variability in PD water potential. PD water potential values were high and relatively constant above soil water content of 0.17 kg kg(-1); below this threshold value the PD water potential declined. Highest positive (r = 0.870) and negative (r = -0.706) correlation coefficients of PD water potential data were observed with soil moisture content at the 20-30 cm soil layer and VPD, respectively. MD water potential, VPD, and air temperature explained about 83% of the variation in PD water potential. Soil water content at the 20-30 cm soil layer, PD water potential, and relative humidity described about 82% of the variation in MD water potential. It was concluded A. berlandieri can endure substantial drydown periods and its water relations are strongly associated with soil water content and atmospheric evaporative demand components.