The objective of this paper is to analyse the differences in price-cost margins of the export and domestic markets for Spanish export manufacturing firms in the period 1990-1997. The estimation of a multiproduct cost function permits us to obtain the marginal costs and the margins of the firms for both markets. Some results emerge from the estimations. First, marginal costs associated to export are bigger than domestic ones and the price-cost margins in domestic markets are larger throughout the period. Second, price-cost margins are procyclical in the domestic market but there is not evidence of this behaviour in the foreign markets. Third, there is not evidence about that the devaluations of the peseta in 1992 and 1993 were used by export firms to increase their margins. Finally, price-cost margins reveal some degree of heterogeneity across industries in both markets.