The econometric estimation of e1asticities of factor demand in Philippine agriculture is studied in this paper. The central purpose of this work is to provide the parameters required for incorporation into a large, applied general equilibrium model of the Philippine economy, known as APEX. The values of these supply side parameters are crucial for the performance of general equilibrium systems like APEX, but the econometric literature offers several alternative possible methodologies for their estimation. These include both primal and dual methods. The first objective of this paper, therefore, is to attempt to discriminate a1ong these alternative methodologies according to the predictive performance of the estimates that they produce. A second objective is to exan1ine the sensitivity of the resulting general equilibrium model to factor demand elasticity estin1ates derived from these alternative methodologies by rr1eans of experiments on the economic effects of technical change in Philippine agriculture.