Water deficit, i.e., rainfall amounts and distribution, is the most common abiotic stress that limits peanut production worldwide. Even though extensive research efforts have been made to improve drought tolerance in peanut, performance of genotypes largely depends upon the environment in which they grow. Based on greenhouse experiments, it has been hypothesized that stomata closure under high vapor pressure deficit (VPD) is a mechanism of soil water conservation and it has been shown that genotypic variation for the response of transpiration rate to VPD in peanut exists. The objective of this study was to determine the relationship between stomatal conductance (g s ) and VPD for field grown peanut in Virginia-Carolina (VC) rainfed environments. In 2009, thirty virginia-type peanut cultivars and advanced breeding lines were evaluated for g s at several times before and after rain events, including a moisture stress episode. In 2010, eighteen genotypes were evaluated for g s under soil water deficit. In 2009, VPD ranged from 1.3 to 4.2 kPa and in 2010 from 1.78 to 3.57 kPa. Under water deficit, genotype and year showed a significant effect on g s (P 5 0.0001), but the genotype 3 year interaction did not. During the water deficit episodes while recorded g s values were relatively high, g s was negatively related to VPD (R 2 5 0.57, n 5 180 in 2009; R 2 5 0.47, n 5 108 in 2010), suggesting that stomata closure is indeed a water conservation mechanism for field grown peanut. However, a wide range of slopes among genotype were observed in both years. Genotypes with significant negative relationships of g s and VPD under water deficit in both years were Florida Fancy, Gregory, N04074FCT, NC-V11, and VA-98R. While Florida Fancy, Gregory, and NC-V11 are known to be high yielding cultivars, VA-98R and line N04074FCT are not. The benefit of stomatal closure during drought episodes in the VC environments is further discussed in this paper.Key Words: Peanut, stomatal conductance, transpiration, vapor pressure deficit.In the Virginia-Carolina (VC) area, peanut is an important cash crop. According to the United Nations Conference on Desertification (UNEP, 1992), this region is characterized as a moist subhumid to humid region. This classification is based on the climatic aridity index: P/ETP, where P is annual precipitation and ETP is annual potential evapotranspiration calculated by the method of Penman (Doorenbos and Pruitt, 1977). Under historically moist conditions, over 90% of the current peanut farming is rainfed in the VC area. However, increased frequency and intensity of dry spells were recently observed due to uneven precipitation distribution during the summer months with negative effects on peanut yield and quality in the VC region. To increase peanut production under rainfed cropping systems in dry years, peanut cultivars with more effective use of water need to be developed for this region.In peanut (Devi et al., 2010) and soybean [Glycine max (L.) Merr.] (Fletcher et al., 2007;Sinclair et al., 2008;Sado...