Here we compare the stomatal conductance (g(s)) values obtained with leaf porometer and infra-red gas analyzer (IRGA) in different species subjected to different water availability and evaluated in two different environmental conditions. Sunflower, maize, bean, and grapevine were subjected to two treatments of water availability: well-watered and progressive water stress for 3 days and evaluated in two different times with contrasting environmental conditions. The g(s) was determined both on the abaxial and adaxial side of leaves using a leaf porometer and an IRGA. The measured g(s) strongly differed between IRGA and porometer, in a way that depended on the species, as well as water availability and environmental conditions. Under maximum water stress, g(s) measured with leaf porometer was higher than those measured with IRGA in the four species studied. The present results question the use of usual methodologies for the estimation of g(s), suggesting that g(s) would not only depend on the environmental conditions and the water status of the plants, but also on the method used to measure it.