In order to sustain plant growth and hydration, water must be continuously supplied to the leaf as it is lost by transpiration. This becomes especially difficult under low soil moisture conditions. The objective of this investigation was to compare peanut (Arachis hypogaea L.) genotypes for their ability to maintain water supply to leaves by measuring apparent sap velocity (V_a) under water stress conditions. V_a was determined by the thermoelectric heat pulse method. Three genotypes (Chico, Florunner, and PI 355993) that differed in rooting traits were studied in the greenhouse. Plants were grown in fritted clay in PVC tubes (10.2 cm inside diameter and 76.2 cm in length). Six genotypes, including Chico and PI 355993, were studied in the field. Soil type was Teller sandy loam (fine, mixed, thermic, Udic Argiustoll). Under control conditions in the greenhouse and irrigated conditions in the field, V_a ranged from about 0.8 to 1.1 cm/min for all genotypes. As water was withheld, V_a declined with time in the greenhouse and was significantly lower under rainfed (-0.25 MPa soil potential) than irrigated (-0.10MPa soil potential) conditions in the field. Significant genotypic differences were found in both greenhouse and field experiments. Chico maintained the highest V_a ratio (stress V_a/control V_a) in the greenhouse. PI 404021, Chico, and PI 355993 showed the least reduction (20, 26, and 29%, respectively) in V_a under rainfed conditions in the field. Thus, the data are indicative of differences among peanut genotypes in maintaining V_a under stress conditions. Knowledge of V_a could be useful in determining relationships between root activity, soil water content, and water uptake and in selecting genotypes for inclusion in breeding programs to develop cultivars that avoid drought stress.