This paper analyses the main determinants of the regional allocation of infrastructure investment. The estimated investment equation is derived from a general specification of the government's objective function (Berhman and Craig, Am. Econom. Rev. 77 (1987) 315), which accounts both for the equity-efficiency trade-off and for deviations from this rule that arise because of political factors. The reaction of investment to changes in the regional output provides information about the strength of the equity-efficiency trade-off. The main political factor considered is a measurement of the electoral productivity of funds invested in each region.