This paper`s main goal is to estimate the elasticity of substitution of non-tradable goods, paying special attention to empirical problems related to time-varying parameters, missing regressors and model misspecification. To that end, the paper creates a database and estimates, via three alternative methods, quarterly series of consumption and prices of tradable and non-tradable goods for Uruguay for the period 1983-2002. The econometric estimations of the parameter of interest were performed with VEC models. These estimates give a long-run elasticity of substitution of %0. 46 in the principal model and %0. 71 and %0. 75 in the two alternative models. Parametric stability tests are performed on the principal model, and the predictive ability of the model is also tested. It is concluded that, not only is the parameter of interest stable over time, but the model also has good predictive properties, even when tested in a very demanding environment: the period following Uruguay`s change of exchange rate regime in mid-2002.