The coupled model of assimilation and stomatal conductance (A-g s) was evaluated to estimate leaf stomatal conductance of a drip-irrigated vineyard (Vitis vinifera L. cv. Cabernet Sauvignon) located in the Pencahue Valley (35°22’ S, 71°47’ W, 150 m.a.s.l.), Maule Region, Chile, during the 2003-2004 and the 2004-2005 growing seasons. Additionally, a calibration of the three parameters mesophyll conductance (g m), maximum specific humidity (Dmax) and coupled factor (f0) was applied on vines growing in 35 L pots. An infrared gas analyzer was used to calibrate and evaluate the A-g s which allowed simultaneous measuring of the leaf net CO2 assimilation (A) and stomatal conductance (g s) in 2 to 3 h intervals of time. The calibration indicated that the g m,, Dmax and f0 values were 1.15 mm s-1, 52.31 g kg-1 and 0.90, respectively. The validation in the drip-irrigated vineyard indicated that the A-g s model was able to estimate the leaf stomatal conductance with a root mean square error (RMSE) of 0.05 mol m-2 s-1, model efficiency of 61% and agreement index of 90%. The sensitivity analysis indicated that the A-g s model is affected considerably by the g m, Dmax and f0 parameterization.