"Mexico's experience before and after trade liberalization presents a challenge to neoclassical trade theory. Though labor abundant, it nevertheless exported skill-intensive goods and protected labor-intensive sectors prior to liberalization. Post-liberalization, the relative wage of skilled workers rose. Courant and Deardorff (1992) have shown theoretically that an extremely uneven distribution of factors within a country can induce behavior at odds with overall comparative advantage. We demonstrate the importance of this insight for developing countries. We show that Mexican regions exhibit substantial variation in skill abundance, offer significantly different relative factor rewards, and produce disjoint sets of industries. This heterogeneity helps to both undermine Mexico's aggregate labor abundance and motivate behavior that is more consistent with relative skill abundance"--National Bureau of Economic Research web site.