Abstract. This paper examines the impact of public infrastructures on the performance of Spanish private business at a disaggregated industry level. We use duality theory to recover the productivity effects of public capital by calculating the cost saving effects that are associated to public services. Using a translog cost function we present panel estimates for 14 Spanish industries during the period 1980-1991. Our results strongly suggest that public capital formation can be considered to be an instrument to improve competitiveness by reducing production costs. However, the results also indicate that there is a technologically induced labor saving effect through higher public investment. Furthermore, our estimates suggest that a distinction among industries is of importance because the effects of public infrastructures vary across industries considerably.